Psychology
by Robert Sessions Woodworth · English · Gutenberg #31382 · 1,050,607 chars · public domain (US)
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Title: Psychology
A study of mental life
Author: Robert Sessions Woodworth
Release date: February 25, 2010 [eBook #31382]
Language: English
Other information and formats: www.gutenberg.org/ebooks/31382
Credits: Produced by Don Kostuch
*** START OF THE PROJECT GUTENBERG EBOOK PSYCHOLOGY ***
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[Transcriber's notes]
This text is derived from an unedited version in the Internet Archive.
Page numbers are indicated by numbers enclosed in curly braces,
e.g. {99}. They have been located where page breaks occurred in the
original book.
Labels and text in a figure that are not mentioned in the figure
description are included as a comma separated list, as in "(Figure
text: cochlea, vestibule, 3 Canals)".
Lengthy footnotes and quotations are indented.
Obvious misspellings and typos are corrected but inconsistent spelling
is not resolved, as in coordinate and coördinate.
Here are the definitions of some unfamiliar words (to me).
amour propre
self-esteem; self-respect.
esprit de corps
camaraderie, bonding, solidarity, fellowship.
motility (motile)
moving or capable of moving spontaneously.
unwonted
unusual.
[End Transcribers's notes]
PSYCHOLOGY
A STUDY OF MENTAL LIFE
BY
ROBERT S. WOODWORTH, Ph. D.
_Professor of Psychology in Columbia University_
NEW YORK
HENRY HOLT AND COMPANY
1921
COPYRIGHT, 1921
BY
HENRY HOLT AND COMPANY
Printed in the U.S.A.
PREFACE
A few words to the reader are in order. In the first place, something
like an apology is due for the free way in which the author has drawn
upon the original work of many fellow-psychologists, without any
mention of their names. This is practically unavoidable in a book
intended for the beginner, but the reader may well be informed of the
fact, and cautioned not to credit the content of the book to the
writer of it. The author's task has been that of selecting from the
large mass of psychological information now available, much of it new,
whatever seemed most suitable for introducing the subject to the
reader. The book aims to represent the present state of a very active
science.
Should the book appear unduly long in prospect, the longest and most
detailed chapter, that on Sensation, might perfectly well be omitted,
on the first reading, without appreciably disturbing the continuity of
the rest.
On the other hand should any reader desire to make this text the basis
of a more extensive course of reading, the lists of references
appended to the several chapters will prove of service. The books and
articles there cited will be found interesting and not too technical
in style.
Much advantage can be derived from the use of the "Exercises". The
text, at the best, but provides raw material. Each student's finished
product must be of his own making. The exercises afford opportunity
for the student to work over the material and make it his own.
A first or preliminary edition of this book, in mimeographed sheets,
was in use for two years in introductory classes conducted by the
author and his colleagues, and was subjected to exceedingly helpful
criticism from both teachers and students. The revision of that
earlier edition into the present form has been very much of a
coöperative enterprise, and so many have coöperated that room could
scarcely be found for all their names. Professor A. T. Poffenberger,
Dr. Clara F. Chassell, Dr. Georgina I. Gates, Mr. Gardner Murphy, Mr.
Harold E. Jones and Mr. Paul S. Achilles have given me the advantage
of their class-room experience with the mimeographed book. Dr.
Christine Ladd-Franklin has very carefully gone over with me the
passages dealing with color vision and with reasoning. Miss Elizabeth
T. Sullivan, Miss Anna B. Copeland, Miss Helen Harper and Dr. A. H.
Martin have been of great assistance in the final stages of the work.
Important suggestions have come also from several other universities,
where the mimeographed book was inspected.
R. S. W.
Columbia University
August, 1921
CONTENTS
CHAPTER I
PAGE
WHAT PSYCHOLOGY IS AND DOES 1
Varieties of Psychology 2
Psychology as Related to Other Sciences 5
The Science of Consciousness 7
The Science of Behavior 8
Introspection 10
Objective Observation 11
General Lines of
Psychological Investigation 14
Summary and Attempt at a Definition 17
Exercises 19
References 20
CHAPTER II
REACTIONS 21
The Reaction Time Experiment 22
Reflex Action 24
The Nerves in Reflex Action 26
Internal Construction of the
Nerves and Nerve Centers 31
The Synapse 34
Coördination 37
Reactions in General 39
Exercises 42
References 44
CHAPTER III
REACTIONS OF DIFFERENT LEVELS 45
Different Sorts of Stimuli 47
The Motor Centers, Lower and Higher 49
How the Brain Produces
Muscular Movements 53
Facilitation and Inhibition 54
Super-motor Centers in the Cortex 56
Speech Centers 57
The Auditory Centers 59
The Visual Centers 62
Cortical Centers for the Other Senses 68
Lower Sensory Centers 64
The Cerebellum 66
Different Levels of Reaction 65
Exercises 67
References 67
CHAPTER IV
TENDENCIES TO REACTION 68
Purposive Behavior 70
Organic States that Influence Behavior 72
Preparation for Action 74
Preparatory Reactions 77
What the Preparatory
Reactions Accomplish 79
What a Tendency Is,
in Terms of Nerve Action 82
Motives 84
Exercises 86
References 88
CHAPTER V
NATIVE AND ACQUIRED TRAITS 89
The Source of Native Traits 90
Reactions Appearing at
Birth Must Be Native 91
Reactions That Cannot Be
Learned Must Be Native 92
Experimental Detection
of Native Reactions 93
Is Walking Native or Acquired? 95
Universality as a Criterion
of Native Reactions 97
Some Native Traits Are
Far from Being Universal 98
Why Acquired Traits Differ from
One Individual to Another 99
What Mental Traits Are Native? 100
Exercises 103
References 104
CHAPTER VI
INSTINCT 105
The Difference Between
an Instinct and a Reflex 107
An Instinct Is a Native
Reaction-Tendency 109
Fully and Partially
Organized Instincts 111
Instincts Are Not Ancestral Habits 113
Instincts Not Necessarily Useful
in the Struggle for Existence 114
The So-called Instincts of
Self-preservation and of Reproduction 115
Exercises 117
References 117
CHAPTER VII
EMOTION 118
Organic States That Are
Not Usually Classed as Emotions 119
How These Organic States
Differ from Regular Emotions 120
The Organic State in Anger 121
Glandular Responses During Emotion 122
The Nerves Concerned in
Internal Emotional Response 124
The Emotional State as
a Preparatory Reaction 125
"Expressive Movements," Another
Sort of Preparatory Reactions 126
Do Sensations of These Various
Preparatory Reactions Constitute
the Conscious State of Emotion? 128
The James-Lange Theory of the Emotions 129
Emotion and Impulse 130
Emotion Sometimes Generates Impulse 132
Emotion and Instinct 134
The Higher Emotions 136
Exercises 136
References 136
CHAPTER VIII
INVENTORY OF HUMAN INSTINCTS
AND PRIMARY EMOTIONS 137
Classification 138
Responses to Organic Needs 139
Instinctive Responses to Other Persons 145
The Play Instincts 151
Exercises 170
References 171
CHAPTER IX
THE FEELINGS 172
Pleasantness and Unpleasantness
Are Simple Feelings 173
Felling-tone of Sensations 174
Theories of Feeling 175
Sources of Pleasantness
and Unpleasantness 178
Primary Likes and Dislikes 180
Other Proposed Elementary Feelings 184
Exercises 186
References 186
CHAPTER X
SENSATION 187
The Sense Organs 188
Analysis of Sensations 197
The Skin Senses 197
The Sense of Taste 201
The Sense of Smell 203
Organic Sensations 204
The Sense of Sight 204
Simpler Forms of the Color Sense 209
Visual Sensations as
Related to the Stimulus 212
Color Mixing 214
What Are the Elementary
Visual Sensations? 216
Theories of Color Vision 220
Adaptation 224
Rod and Cone Vision 226
After-images 226
Contrast 227
The Sense of Hearing 228
Comparison of Sight and Hearing 231
Theory of Hearing 234
Senses of Bodily Movement 236
Exercises 241
References 243
CHAPTER XI
ATTENTION 244
The Stimulus, or
What Attracts Attention 245
The Motor Reaction in Attention 248
The Shifting of Attention 251
Laws of Attention and
Laws of Reaction in General 256
Sustained Attention 257
Distraction 259
Doing Two Things at Once 260
The Span of Attention 261
Summary of the Laws of Attention 262
Attention and Degree of Consciousness 265
The Management of Attention 267
Theory of Attention 268
Exercises 270
References 270
CHAPTER XII
INTELLIGENCE 271
Intelligence Tests 272
Performance Tests 275
Group Testing 276
Some Results of the Intelligence Tests 278
Limitations of the Intelligence Tests 281
The Correlation of Abilities 288
General Factors in Intelligence 285
Special Aptitudes 288
Heredity of Intelligence
and of Special Aptitudes 289
Intelligence and the Brain 292
Exercises 294
References 295
CHAPTER XIII
LEARNING AND HABIT FORMATION 296
Acquired Reactions Are
Modified Native Reactions 297
Acquired Tendencies 299
Animal Learning 302
Summary of Animal Learning 310
Human Learning 311
Human Compared with Animal Learning 313
Learning by Observation 317
The Learning of Complex
Practical Performances 321
Higher Units and Overlapping 323
Moderate Skill Acquired in
the Ordinary Day's Work 326
Habit 328
Exercises 330
References 331
CHAPTER XIV
MEMORY 332
The Process of Memorizing 333
Economy in Memorizing 333
Unintentional Learning 346
Retention 348
Recall 364
Recognition 357
Memory Training 360
Exercises 364
References 365
CHAPTER XV
ASSOCIATION AND MENTAL IMAGERY 366
What Can Be Recalled 366
Memory Images 368
Limitations of Imagery 371
The Question of Non-Sensory Recall 373
Hallucinations 375
Free Association 376
Controlled Association 381
Examples of Controlled Association 384
Exercises 386
References 388
CHAPTER XVI
THE LAWS OF ASSOCIATION 389
The Law of Exercise 389
The Law of Effect 391
Limitations of the Law of Exercise 393
Association by Similarity 395
Association by Contiguity 396
The Law of Combination 398
The Law of Combination in Recall 413
The Laws of Learning in
Terms of the Neurones 414
Exercises 418
References 418
CHAPTER XVII
PERCEPTION 418
Some Definitions 421
The Difference Between
Perception and Sensation 423
Perception and Image 425
Perception and Motor Reaction 427
What Sort of Response,
Then, Is Perception? 431
Practiced Perception 433
Corrected Perception 435
Sensory Data Serving as Signs
of Various Sorts of Fact 437
The Perception of Space 439
Esthetic Perception 443
Social Perception 444
Errors of Perception 446
Illusions 450
Exercises 460
References 461
CHAPTER XVIII
REASONING 462
Animal and Human Exploration 463
Reasoning Culminates in Inference 465
Varieties of Reasoning 468
Deductive and Inductive Reasoning 474
Psychology and Logic 476
Exercises 480
References 480
CHAPTER XIX
IMAGINATION 481
Beginnings of Imagination
in the Child 482
Preliminary Definition of Imagination 483
Play 485
The Play Motives 488
Empathy 491
Worry 497
Day Dreams 498
Dreams 499
Freud's Theory of Dreams 505
Autistic Thinking 508
Invention and Criticism 509
The Enjoyment of Imaginative Art 512
The Psychology of Inventive Production 517
Imagination Considered in General 519
Exercises 521
References 522
CHAPTER XX
WILL 523
Voluntary and Involuntary Action 524
Development of Voluntary Control 526
Ideomotor Action 527
Conflict and Decision 528
Obstruction and Effort 535
Thought and Action 539
Securing Action 541
The Influence of Suggestion 546
Exercises 551
References 561
CHAPTER XXI
PERSONALITY 552
Factors in Personality 553
The Self 555
Integration and Disintegration
of the Personality 558
The Unconscious, or,
the Subconscious Mind 561
Unconscious Wishes and Motives 565
Exercises 571
References 571
INDEX 573
{1}
PSYCHOLOGY
CHAPTER I
WHAT PSYCHOLOGY IS AND DOES
THE SUBJECT-MATTER OF THE SCIENCE, ITS PROBLEMS AND ITS METHODS
Modern psychology is an attempt to bring the methods of scientific
investigation, which have proved immensely fruitful in other fields,
to bear upon mental life and its problems. The human individual, the
main object of study, is so complex an object, that for a long time it
seemed doubtful whether there ever could be real science here; but a
beginning was made in the nineteenth century, following the lead of
biology and physiology, and the work of the investigator has been so
successful that to-day there is quite a respectable body of knowledge
to assemble under the title of scientific psychology.
Psychology, then, is a science. It is the science of--what shall we
say? "The science of the soul"--that is what the name means by
derivation and ancient usage. "The science of the mind" has a more
modern sound. "The science of consciousness" is more modern still.
"The science of behavior" is the most recent attempt at a concise
formula.
None of these formulas is wholly satisfactory. Psychology does not
like to call itself the science of the soul, for that has a
theological tang and suggests problems that have so far not seemed
accessible to scientific investigation. Psychology does not like very
well to call itself the science {2} of the mind, as _the_ mind seems to
imply some thing or machine, and there is no such thing to be observed
(unless it be the brain and body generally), and, anyway, psychology
is distinctly a study of actions rather than of things. Psychology
does not like to limit itself to the study of consciousness, but finds
it necessary to study also unconscious actions. As to "behavior", it
would be a very suitable term, if only it had not become so closely
identified with the "behavioristic movement" in psychology, which
urges that consciousness should be entirely left out of psychology, or
at least disregarded. "Behavior psychology", as the term would be
understood to-day, means a part of the subject and not the whole.
[Footnote: A series of waggish critics has evolved the following:
"First psychology lost its soul, then it lost its mind, then it lost
consciousness; it still has behavior, of a kind."]
The best way of getting a true picture of psychology, and of reaching
an adequate definition of its subject-matter, would be to inspect the
actual work of psychologists, so as to see what kind of knowledge they
are seeking. Such a survey would reveal quite a variety of problems
under process of investigation, some of them practical problems,
others not directly practical.
Varieties of Psychology
Differential psychology.
One line of question that always interests the beginner in psychology
is as to how people differ--how different people act under the same
circumstances--and why; and if we watch the professional
psychologist, we often find him working at just this problem. He tests
a great number of individuals to see how they differ, and tries to
discover on what factors their differences depend, how far on
heredity, how far on environment. The "psychologist" in such a place
as the children's court {3} is a specialist whose duty it is to test
the delinquent children that are brought before the court, with the
special object of measuring the intelligence of each individual child
and of helping in other ways to understand the child's peculiar
conduct and attitude.
The "psychological examiner" in the Army, during the Great War, had the
same general object in view. It was desirable to measure the
intelligence of each recruit as he entered the service, since military
experience had shown that men of low intelligence made poor soldiers,
while those of high intelligence made the best officers and
non-commissioned officers, provided they also possessed good physique
and certain less measureable mental qualifications, such as courage
and leadership.
Applied psychology.
The Army psychologists, like the court psychologist, were engaged in
applying scientific knowledge to the practical problems of life; and
there are many other applications of psychology, to education, to
medicine, to business and other occupations, as well as to the art of
right living. Scientific knowledge enables you to _predict_ and
_control_. Having devised scientific tests for intelligence, you can
predict of a six-year-old boy who tests low, that he will not get much
good from the regular classes in school; and thus you are in a
position to control the education of this boy for his own best
interests. In the Army, it happened during the earlier part of the war
that some companies or regiments made much slower progress in training
than others; and a whole Division was delayed for months because of
the backwardness of a single regiment. When the psychological tests
were introduced, these slow-learning units were found to contain a
disproportionate number of men of low intelligence. From that time on,
it was possible by aid of the tests to equalize the intelligence of
different units when first formed, and thus insure equal {4} progress
in training. This was a good example of "control".
Most of us are attracted by the practical use of a science, and some
have no patience with any study that does not seem immediately
practical. But really any science, however much it is applied, must
remain fundamentally a pure science; that is, it must seek most of all
to know and understand. Practical scientific knowledge was usually
first obtained without any inkling of how it might be used. The
science of electricity is the most striking example of this. It began
as an attempt to understand certain curious phenomena, which seemed to
be nothing but curiosities; yet when the knowledge of these phenomena
had progressed to a certain point, abundant use was found for it. Much
the same is true of psychology, which began as a pure science and only
recently has found ways of applying its discoveries to practical
affairs. So the student beginning the science, though properly
desirous of making practical use of what he learns, should let himself
be governed for the present by the desire to know and understand,
confident that the more scientific (which is to say, the more
complete, systematic and reliable) his knowledge is, the more
available it will be for practical application.
General psychology.
Our science is not concerned entirely with differences between people,
but asks also in what ways people are alike, and this is indeed its
central problem. How do "we" observe, learn, remember, imagine, think?
What sensations and feelings do we have, what emotions, what
instincts, what natural and acquired impulses to action? How are our
natural powers and impulses developed and organized as we grow up?
Psychology is concerned with the child as well as the adult, and it is
even concerned with the animal. It is concerned with the abnormal as
well as the normal human being. So you will find books and {5} courses
on animal psychology, child psychology, abnormal psychology. Now
general psychology--or just plain "psychology"--has to do with the
main laws and principles that hold in all these special fields.
Psychology as Related to Other Sciences
A good definition of our science would distinguish it from other
sciences, especially from those neighboring sciences with which it is
in closest contact.
Psychology and sociology.
There is no difficulty in framing a good logical distinction here.
Sociology studies the activities of a group of people taken as a
whole, while psychology studies the activities of the individuals.
Both might be interested in the same social act, such as an election,
but sociology would consider this event as a unit, whereas psychology
would break it up into the acts of the several voters. The distinction
is clear enough theoretically, but breaks down often in practice, as
sociology would like to know the motives that swayed individual
voters, while psychology on its side is interested to know what
decision was reached by the majority. All the social sciences,
including economics and politics, have a psychological side, since
they evidently are concerned to know the causes that govern human
conduct. Social psychology studies the individual in his social
relations.
Psychology and biology.
Biology, being the science of living creatures, includes psychology,
which studies these creatures on the mental side. The science of life
includes the science of mental life. We may call psychology a part of
biology, or we may call it one of the biological sciences. It has very
close contact with several other branches of biology. Animal
psychology overlaps that part of zoology which studies the behavior of
animals. Genetic psychology, as it is sometimes called, i.e., the
study of mental heredity. {6} and development, dovetails with the
general biological science of genetics, so that we find biologists
gathering data on the heredity of feeble-mindedness or of musical
ability, while psychologists discuss the general theory of heredity.
Psychology and physiology.
That one of all the sciences that has the closest contacts with
psychology is human and animal physiology. Broadly defined, physiology
is that part of biology that studies functions or activities; and, so
defined, it includes psychology as part of itself. In practice,
psychology devotes itself to desire, thought, memory, and such "mental
functions", while physiology concentrates its effort upon "bodily
functions" like digestion and circulation. But this is only a rough
distinction, which breaks down at many points.
Where shall we class sensation? Is it "mental" or "bodily"? Both
sciences study it. Physiology is perhaps more apt to go into the
detailed study of the action of the sense organs, and psychology to
concern itself with the classification of sensations and the use made
of them for recognizing objects or for esthetic purposes. But the line
between the two sciences is far from sharp at this point.
Speech, also, lies in both provinces. Physiology has studied the
action of the vocal organs and the location of the brain centers
concerned in speech, while psychology has studied the child's process
of learning to speak and the relation of speech to thought, and is
more apt to be interested in stuttering, slips of the tongue, and
other speech disturbances which are said to be "mental rather than
physical".
It would be hard to mention any activity that is mental without being
physical at the same time. Even thinking, which seems as purely mental
as any, requires brain action; and the brain is just as truly a bodily
organ as the heart or stomach. Its activity is bodily activity and
lies properly within the field of physiology.
{7}
But it would be equally difficult to mention any function that is
exclusively bodily, and not mental at the same time, in some degree.
Take digestion for example: the pleasant anticipation of food will
start the digestive juices flowing, before any food is physically in
the stomach; while in anger or fear digestion comes to a sudden halt.
Therefore we find physiologists interested in these emotions, and
psychologists interested in digestion.
We do not find any clean separation between our science and
physiology; but we find, on the whole, that psychology examines what
are called "mental" activities, and that it studies them as the
performances of the whole individual rather than as executed by the
several organs.
The Science of Consciousness
Typically, the activities that psychology studies are conscious
performances, while many of those falling to physiology are
unconscious. Thus digestion is mostly unconscious, the heart beat is
unconscious except when disturbed, the action of the liver is entirely
unconscious. Why not say, then, that psychology is the study of
conscious activities?
There might be some objection to this definition from the side of
physiology, which studies certain conscious activities itself--speech,
for example, and especially sensation.
There would be objection also from the side of psychology, which does
not wish to limit itself to conscious action. Take the case of any act
that can at first be done only with close attention, but that becomes
easy and automatic after practice; at first it is conscious, later
unconscious, but psychology would certainly need to follow it from the
initial to the final stage, in order to make a complete study of the
practice effect. And then there is the "unconscious", or the
"subconscious mind"--a matter on which psychologists {8} do not wholly
agree among themselves; but all would agree that the problem of the
unconscious was appropriate to psychology.
For all the objections, it remains true that the _typical_ mental
process, the typical matter for psychological study, is conscious.
"Unconscious mental processes" are distinguished from the unconscious
activity of such organs as the liver by being somehow _like_ the
conscious mental processes.
It would be correct, then, to limit psychology to the study of
conscious activities and of activities akin to these.
The Science of Behavior
No one has objected so strenuously to defining psychology as the
science of consciousness, and limiting it to consciousness, as the
group of animal psychologists. By energetic work, they had proved that
the animal was a very good subject for psychological study, and had
discovered much that was important regarding instinct and learning in
animals. But from the nature of the case, they could not observe the
consciousness of animals; they could only observe their behavior, that
is to say, the motor (and in some cases glandular) activities of the
animals under known conditions. When then the animal psychologists
were warned by the mighty ones in the science that they must interpret
their results in terms of consciousness or not call themselves
psychologists any longer, they rebelled; and some of the best fighters
among them took the offensive, by insisting that human psychology, no
less than animal, was properly a study of behavior, and that it had
been a great mistake ever to define it as the science of
consciousness.
It is a natural assumption that animals are conscious, but after all
you cannot directly observe their consciousness, and you cannot
logically confute those philosophers {9} who have contended that the
animal was an unconscious automaton. Still less can you be sure in
detail what is the animal's sensation or state of mind at any time; to
get at that, you would need a trustworthy report from the animal
himself. Each individual must observe his own consciousness; no one
can do it from outside. The objection of the behaviorist to
"consciousness psychology" arises partly from distrust of this method
of inner observation, even on the part of a human observer.
Indeed, we can hardly define psychology without considering its
_methods of observation_, since evidently the method of observation
limits the facts observed and so determines the character of the
science. Psychology has two methods of observation.
When a person performs any act, there are, or may be, two sorts of
facts to be observed, the "objective" and the "subjective". The
objective facts consist of movements of the person's body or of any
part of it, secretions of his glands (as flow of saliva or sweat), and
external results produced by these bodily actions--results such as
objects moved, path and distance traversed, hits on a target, marks
made on paper, columns of figures added, vocal or other sounds
produced, etc., etc. Such objective facts can be observed by another
person.
The subjective facts can be observed only by the person performing the
act. While another person can observe, better indeed than he can
himself, the motion of his legs in walking, he alone can observe the
sensations in the joints and muscles produced by the leg movement. No
one else can observe his pleased or displeased state of mind, nor
whether he is thinking of his walking or of something quite different.
To be sure, his facial expression, which is an objective fact, may
give some clue to his thoughts and feelings, but "there's no art to
read the mind's construction {10} in the face", or at least no sure
art. One may feign sleep or absorption while really attending to what
is going on around. A child may wear an angelic expression while
meditating mischief. To get the subjective facts, we shall have to
enlist the person himself as our observer.
Introspection
This is observation by an individual of his own conscious action. It
is also called subjective observation. Notice that it is a form of
observation, and not speculation or reasoning from probabilities or
from past experience. It is a direct observation of fact.
One very simple instance of introspection is afforded by the study of
after-images. Look for an instant at the glowing electric bulb, and
then turn your eyes upon a dark background, and observe whether the
glowing filament appears there; this would be the "positive
after-image". This simple type of introspection is used by physiology
in its study of the senses, as well as by psychology; and it gives
such precise and regular results that only the most confirmed
behaviorists refuse to admit it as a good method of observation.
But psychology would like to make introspective observations on the
more complex mental processes as well; and it must be admitted that
here introspection becomes difficult. You cannot hope to make minute
observations on any process that lasts over a very few seconds, for
you must let the process run its natural course unimpeded by your
efforts at observing it, and then turn your "mental eye" instantly
back to observe it _retrospectively_ before it disappears. As a matter
of fact, a sensation or feeling or idea hangs on in consciousness for
a few seconds, and can be observed in this retrospective way. There is
no theoretical objection to this style of introspection, but it is
practically difficult and {11} tricky. Try it on a column of figures:
first add the column as usual, then immediately turn back and review
exactly what went through your mind in the process of adding---what
numbers you spoke internally, etc. Try again by introspecting the
process of filling in the blanks in the sentence:
"Botany could not make use of introspection because ______ have
probably no ________ processes."
At first, you may find it difficult to observe yourself in this way;
for the natural tendency, when you are aiming at a certain result, is
to reach the goal and then shift to something else, rather than to
turn back and review the steps by which you reached the goal. But with
practice, you acquire some skill in introspection.
One difficulty with introspection of the more complex mental processes
is that individuals vary more here than in the simpler processes, so
that different observers, observing each his own processes, will not
report the same facts, and one observer cannot serve as a check upon
another so easily as in the simpler introspection of after-images and
other sensations, or as in the observations made in other sciences.
Even well trained introspectionists are quite at variance when they
attempt a minute description of the thought processes, and it is
probable that this is asking too much of introspection. We mustn't
expect it to give microscopic details. Rough observations, however, it
gives with considerable certainty. Who can doubt, for example, that a
well-practised act goes on with very little consciousness, or that
inner, silent speech often accompanies thinking? And yet we have only
introspection to vouch for these facts.
Objective Observation
But to say, as used to be said, that psychology is purely an
introspective science, making use of no other sort of observation, is
absurd in the face of the facts.
{12}
We have animal psychology, where the observation is exclusively
objective. In objective observation, the observer watches something
else, and not himself. In animal psychology, the psychologist, as
observer, watches the animal.
The same is true of child psychology, at least for the first years of
childhood. You could not depend on the introspections of a baby, but
you can learn much by watching his behavior. Abnormal persons, also,
are not often reliable introspectionists, and the study of abnormal
psychology is mostly carried on by objective methods.
Now how is it with the normal adult human being, the standard subject
for psychology? Does he make all the observations on himself or may he
be objectively observed by the psychologist? The latter, certainly. In
fact, nearly all tests, such as those used in studying differential
psychology, are objective. That is to say that the person tested is
given a task to perform, and his performance is observed in one way or
another by the examiner. The examiner may observe the _time_ occupied
by the subject to complete the task, or the _quantity_ accomplished in
a fixed time; or he may measure the correctness and _excellence_ of
the work done, or the _difficulty_ of the task assigned. One test uses
one of these measures, and another uses another; but they are all
objective measures, not depending at all on the introspection of the
subject.
What is true of tests in differential psychology is true of the
majority of experiments in general psychology: the performer is one
person, the observer another, and the observation is objective in
character. Suppose, for example, you are investigating a memory
problem; your method may be to set your subject a lesson to memorize
under certain defined conditions, and see how quickly and well he
learns it; then you give him another, equally difficult lesson to be
learned under altered conditions, and observe whether he {13} does
better or worse than before. Thus you discover which set of conditions
is more favorable for memorizing, and thence can infer something of
the way in which memorizing is accomplished. In the whole experiment
you need not have called on your subject for any introspections; and
this is a type of many experiments in which the subject accomplishes a
certain task under known conditions, and his success is objectively
observed and measured.
There is another type of objective psychological observation, directed
not towards the success with which a task is accomplished, but towards
the changes in breathing, heart beat, stomach movements, brain
circulation, or involuntary movements of the hands, eyes, etc., which
occur during the course of various mental processes, as in reading, in
emotion, in dreaming or waking from sleep.
Now it is not true as a matter of history that either of these types
of objective observation was introduced into psychology by those who
call themselves behaviorists. Not at all; experiments of both sorts
have been common in psychology since it began to be an experimental
science. The first type, the success-measuring experiment, has been
much more used than introspection all along. What the behaviorists
have accomplished is the definitive overthrow of the doctrine, once
strongly insisted on by the "consciousness psychologists", that
introspection is the only real method of observation in psychology;
and this is no mean achievement. But we should be going too far if we
followed the behaviorists to the extent of seeking to exclude
introspection altogether, and on principle. There is no sense in such
negative principles. Let us accumulate psychological facts by any
method that will give the facts.
{14}
General Laws of Psychological Investigation.
Either introspective or objective observation can be employed in the
_experimental attack_ on a problem, which consists, as just
illustrated in the case of memory, in controlling the conditions under
which a mental performance occurs, varying the conditions
systematically, and noting the resulting change in the subject's
mental process or its outcome. Psychologists are inclined to regard
this as the best line of attack, whenever the mental activity to be
studied can be effectively subjected to control. Unfortunately,
emotion and reasoning are not easily brought under control, and for
this reason psychology has made slower progress in understanding them
than it has made in the fields of sensation and memory, where good
experimental procedure has been developed.
Another general line of attack worthy to be mentioned alongside of the
experimental is the _comparative method_. You compare the actions of
individuals, classes or species, noting likenesses and differences.
You see what behavior is typical and what exceptional. You establish
norms and averages, and notice how closely people cluster about the
norm and how far individuals differ from it. You introduce tests of
various sorts, by which to get a more precise measure of the
individual's performance. Further, by the use of what may be called
double comparison, or "correlation", you work out the relationships of
various mental (and physical) traits. For example, when many different
species of animals are compared in intelligence and also in brain
weight, the two are found to correspond fairly well, the more
intelligent species having on the whole the heavier brains; from which
we fairly conclude that the size of the brain has something to do with
intelligence. But when we correlate brain weight and intelligence in
human individuals. {15} we find so many exceptions to the rule (stupid
men with large brains and gifted men with brains of only moderate
size) that we are forced to recognize the importance of other factors,
such as the perfection of the microscopic structure of the brain.
Tests and correlations have become so prominent in recent
psychological investigation that this form of the comparative method
ranks on a par with the strict experimental method. A test is an
experiment, in a way, and at least is often based upon an experiment;
but the difference between the two lines of attack is that an
experiment typically takes a few subjects into the laboratory and
observes how their mental performances change with planfully changed
conditions; whereas a test goes out and examines a large number of
persons under one fixed set of conditions. An experiment belongs under
what we called "general psychology", and a test under "differential
psychology", since the first outcome of a test is to show how the
individual differs from others in a certain respect. The results may,
however, be utilized in various ways, either for such practical
purposes as guiding the individual's choice of an occupation, or for
primarily scientific purposes, such as examining whether intelligence
goes with brain size, whether twins resemble each other as much
mentally as they do physically, whether intellectual ability and moral
goodness tend on the whole to go together, or not.
The _genetic method_ is another of the general lines of attack on
psychological problems. The object here is to trace the mental
development of the individual, or of the race. It may be to trace the
development either of mentality in general, or of some particular
mental performance. It may be to trace the child's progress in
learning to speak, or to follow the development of language in the
human species, from the most primitive tongues up to those of the
great {16} civilized peoples of to-day. It may be to trace the
improvement of a performance with continued practice.
The value of the genetic method is easily seen. Usually the beginnings
of a function or performance are comparatively simple and easy to
observe and analyze. Also, the process of mental growth is an
important matter to study on its own account.
The _pathological method_ is akin to the genetic, but traces the decay
or demoralization of mental life instead of its growth. It traces the
gradual decline of mental power with advancing age, the losses due to
brain disease, and the maladaptations that appear in insanity and
other disturbances. Here psychology makes close contact with
_psychiatry_ which is the branch of medicine concerned with the
insane, etc., and which in fact has contributed most of the
psychological information derived from the pathological method.
The object of the pathological method is, on the one side, to
understand abnormal forms of mental life, with the practical object of
preventing or curing them, and on the other side, to understand normal
mental life the better. Just as the development of a performance
throws light on the perfected act, so the decay or disturbance of a
function often reveals its inner workings; for we all know that it is
when a machine gets out of order that one begins to see how it ought
to work. Failure sheds light on the conditions of success,
maladaptation throws into relief the mental work that has to be done
by the normal individual in order to secure and maintain his good
adaptation. According to the psychiatrists, mental disturbance is
primarily an affair of emotion and desire rather than of intellect;
and consequently they believe that the pathological method is of
special importance in the study of the emotional life.
{17}
Summary and Attempt at a Definition
Having now made a rapid preliminary survey of the field of psychology,
and of the aims and methods of the workers in this field, we ought to
be in a position to give some sort of a definition.
We conclude, then: psychology is a part of the scientific study of
life, being the science of mental life. Life consisting in process or
action, psychology is the scientific study of mental processes or
activities. A mental activity is typically, though not universally,
conscious; and we can roughly designate as mental those activities of
a living creature that are either conscious themselves or closely akin
to those that are conscious. Further, any mental activity can also be
regarded as a physiological activity, in which case it is analyzed
into the action of bodily organs, whereas as "mental" it simply comes
from the organism or individual as a whole. Psychology, in a word, is
the science of the conscious and near-conscious activities of living
individuals.
Psychology is not interested either in dead bodies or in disembodied
spirits, but in living and acting individuals.
One word more, on the _psychological point of view_. In everyday life
we study our acquaintances and their actions from a personal
standpoint. That is, we evaluate their behavior according as it
affects ourselves, or, perhaps, according as it squares or not with
our standards of right and wrong. We always find something to praise
or blame. Now, the psychologist has no concern with praise and blame,
but is a seeker after the facts. He would know and understand human
actions, rather than pass judgment on them. When, for example, he is
introduced into the school or children's court, for the purpose of
examining children that are "problems", his attitude differs
considerably from that of the {18} teacher or officer of the law; for
while they almost inevitably pass judgment on the child in the way of
praise or blame, the psychologist simply tries to understand the
child. The young delinquent brought into the laboratory of the court
psychologist quickly senses the unwonted atmosphere, where he is
neither scolded nor exhorted, but asked to lend his coöperation in an
effort to discover the cause why his conduct is as it is. Now, this
psychological attitude is not necessarily "better" than the other, but
it is distinctly valuable in its place, as seen from the fact that the
young delinquent often does coöperate. He feels that if the
psychologist can find out what is the trouble with him, this may help.
Nothing, indeed, is more probable; it is when we have the facts and
trace out cause and effect that we are in a fair way to do good.
Nothing is more humane than psychology, in the long run, even though
the psychologist may seem unfeeling in the course of his
investigation.
To the psychologist, conduct is a matter of cause and effect, of
natural law. His business is to know the laws of that part of nature
which we call human nature, and to use these laws, as fast as
discovered, for solving the problems presented by the human individual
or group. For him, even the most capricious conduct has its causes,
even the most inexplicable has its explanation--if only the cause can
be unearthed, which he does not pretend he can always actually
accomplish, since causes in the mental realm are often very complex.
No one can be a psychologist all of the time; no one can or should
always maintain this matter-of-fact attitude towards self and
neighbor. But some experience with the psychological attitude is of
practical value to any one, in giving clearer insight, more
toleration, better control, and even saner standards of living.
{19}
EXERCISES
1. Outline the chapter. A sample outline of the briefer sort is
here given:
A. Subject-matter of psychology: mental activities.
(1) A sub-class under vital activities.
(2) Activities of individuals, as distinguished from
(a) Activities of social groups (sociology).
(b) Activities of single organs (physiology).
(3) Either conscious, or closely related to conscious activities.
(4) May be activities of human or animal, adult or child,
normal or abnormal individuals.
B. Problems of psychology:
(1) How individuals differ in their mental activities.
(2) How individuals are alike in their mental activities.
(3) Practical applications of either (1) or (2).
C. Methods of psychology:
(1) Methods of observing mental activities.
(a) Introspective, the observing by an individual of his own actions.
(b) Objective, the observation of the behavior of other individuals.
(2) General lines of attack upon psychological problems.
(a) Experimental: vary the conditions and see how the mental
activity changes.
(b) Comparative: test different individuals or
classes and see how mental activity differs, etc.
(c) Genetic: trace mental development.
(d) Pathological: examine mental decay or disturbance.
2. Formulate a psychological question regarding each of the following:
hours of work, genius, crime, baseball.
3. Distinguish introspection from theorizing.
4. What different sorts of objective fact can be observed in psychology?
5. What is the difference between the physiology of hearing and the
psychology of hearing?
6. State two reasons why it would be undesirable to limit psychology
to the introspective study of consciousness.
{20}
7. What is the difference between an experiment and a test, (a) in
purpose, (b) in method?
8. Compare the time it takes you to add twenty one-place numbers,
arranged in a vertical column, and arranged in a horizontal line,
(a) Is this introspective or objective observation? Why so? (b) Is
it a test or an experiment? Why?
9. Write a psychological sketch of some one you know well, taking
care to avoid praise and blame, and to stick to the psychological
point of view.
REFERENCES
Some of the good books on the different branches of psychology are
the following:
On animal psychology:
Margaret F. Washburn, _The Animal Mind_, 2nd edition, 1917.
John B. Watson, _Behavior_, 1914.
On child psychology:
Norsworthy and Whitley, _The Psychology of Childhood_, 1918.
On abnormal psychology:
A. J. Rosanoff, _Manual of Psychiatry_, 5th edition, 1920.
On applied psychology:
Hollingworth and Poffenberger, _Applied Psychology_, 1917.
On individual psychology, parts of:
E. L. Thorndike, _Educational Psychology, Briefer Course_, 1914,
Daniel Starch, _Educational Psychology_, 1919.
{21}
CHAPTER II
REACTIONS
REFLEXES AND OTHER ELEMENTARY FORMS OF REACTION,
AND HOW THE NERVES OPERATE IN CARRYING THEM OUT
Having the field of psychology open before us, the next question is,
where to commence operations. Shall we begin with memory, imagination
and reasoning, or with will, character and personality, or with motor
activity and skill, or with feelings and emotions, or with sensation
and perceptions? Probably the higher forms of mental activity seem
most attractive, but we may best leave complicated matters till later,
and agree to start with the simplest sorts of mental performance. Thus
we may hope to learn at the outset certain elementary facts which will
later prove of much assistance in unraveling the more complex
processes.
Among the simplest processes are sensations and reflexes, and we might
begin with either. The introspective psychologists usually start with
sensations, because their great object is to describe consciousness,
and they think of sensations as the chief elements of which
consciousness is composed. The behaviorists would prefer to start with
reflexes, because they conceive of behavior as composed of these
simple motor reactions.
Without caring to attach ourselves exclusively to either
introspectionism or behaviorism, we may take our cue just here from
the behaviorists, because we shall find the facts of motor reaction
more widely useful in our further studies than the facts of sensation,
and because the facts of {22} sensation fit better into the general
scheme of reactions than the facts of reaction fit into any general
scheme based on sensation.
A reaction is a _response_ to a _stimulus_. The response, in the
simplest cases, is a muscular movement, and is called a "motor
response". The stimulus is any force or agent that, acting upon the
individual, arouses a response.
If I start at a sudden noise, the noise is the stimulus, and the
forcible contraction of my muscles is the response. If my old friend's
picture brings tears to my eyes, the picture (or the light reflected
from it) is the stimulus, and the flow of tears is the response, here
a "glandular" instead of a motor response.
The Reaction Time Experiment
One of the earliest experiments to be introduced into psychology was
that on reaction time, conducted as follows: The experimenter tells
his "subject" (the person whose reaction is to be observed) to be
ready to make a certain movement as promptly as possible on receiving
a certain stimulus. The response prescribed is usually a slight
movement of the forefinger, and the stimulus may be a sound, a flash
of light, a touch on the skin, etc. The subject knows in advance
exactly what stimulus is to be given and what response he has to make,
and is given a "Ready!" signal a few seconds before the stimulus. With
so simple a performance, the reaction time is very short, and delicate
apparatus must be employed to measure it. The "chronoscope" or clock
used to measure the reaction time reads to the hundredth or thousandth
of a second, and the time is found to be about .15 sec. in responding
to sound or touch, about .18 sec. in responding to light.
Even the simple reaction time varies, however, from one {23}
individual to another, and from one trial to another. Some persons can
never bring their record much below the figures stated, while a few
can get the time down to .10 sec, which is about the limit of human
ability. Every one is bound to vary from trial to trial, at first
widely, after practice between narrow limits, but always by a few
hundredths of a second at the least. It is curious to find the
elementary fact of variability of reaction present in such a simple
performance.
What we have been describing is known as the "simple reaction", in
distinction from other experiments that demand more of the subject. In
the "choice reaction", there are two stimuli and the subject may be
required to react to the one with the right hand and to the other with
the left; for example, if a red light appears he must respond with the
right hand, but if a green light appears, with the left. Here he
cannot allow himself to become keyed up to as high a pitch as in the
simple reaction, for if he does he will make many false reactions.
Therefore, the choice reaction time is longer than the simple reaction
time--about a tenth of a second longer.
The "associative reaction" time is longer still. Here the subject must
name any color that is shown, or read any letter that is shown, or
respond to the sight of any number by calling out the next larger
number, or respond to any suitable word by naming its opposite. He
cannot be so well prepared as for the simple, or choice reaction,
since he doesn't know exactly what the stimulus is going to be; also,
the brain process is more complex here; so that the reaction time is
longer, about a tenth of a second longer, at the best, than the choice
reaction. It may run up to two or three seconds, even in fairly simple
cases, while if any serious thinking or choosing has to be done, it
runs into many seconds and even into minutes. Here the brain process
is very {24} complex and involves a series of steps before the
required motor response can be made.
These laboratory experiments can be paralleled by many everyday
performances. The runner starting at the pistol shot, after the
preparatory "Ready! Set!", and the motorman applying the brakes at the
expected sound of the bell, are making "simple" reactions. The boxer,
dodging to the right or the left according to the blow aimed at him by
his adversary, is making choice reactions, and this type is very
common in all kinds of steering, handling tools and managing
machinery. Reading words, adding numbers, and a large share of simple
mental performances, are essentially associative reactions. In most
cases from ordinary life, the _preparation_ is less complete than in
the laboratory experiments, and the reaction time is accordingly
longer.
Reflex Action
The simple reaction has some points of resemblance with the "reflex",
which, also, is a prompt motor response to a sensory stimulus. A
familiar example is the reflex wink of the eyes in response to
anything touching the eyeball, or in response to an object suddenly
approaching the eye. This "lid reflex" is quicker than the quickest
simple reaction, taking about .05 second. The knee jerk or "patellar
reflex", aroused by a blow on the patellar tendon just below the knee
when the knee is bent and the lower leg hanging freely, is quicker
still, taking about .03 second. The reason for this extreme quickness
of the reflex will appear as we proceed. However, not every reflex is
as quick as those mentioned, and some are slower than the quickest of
the simple reactions.
A few other examples of reflexes may be given. The "pupillary reflex"
is the narrowing of the pupil of the eye {25} in response to a bright
light suddenly shining into the eye. The "flexion reflex" is the
pulling up of the leg in response to a pinch, prick or burn on the
foot. Coughing and sneezing are like this in being protective
reflexes, and the scratching of the dog belongs here also.
There are many internal reflexes: movements of the stomach and
intestines, swallowing and hiccoughing, widening and narrowing of the
arteries resulting in flushing and paling of the skin. These are
muscular responses; and there are also glandular reflexes, such as the
discharge of saliva from the salivary glands into the mouth, in
response to a tasting substance, the flow of the gastric juice when
food reaches the stomach, the flow of tears when a cinder gets into
the eye. There are also inhibitory reflexes, such as the momentary
stoppage of breathing in response to a dash of cold water. All in all,
a large number of reflexes are to be found.
Most reflexes can be seen to be _useful_ to the organism. A large
proportion of them are protective in one way or another, while others
might be called regulative, in that they adjust the organism to the
conditions affecting it.
Now comparing the reflex with the simple reaction, we see first that
the reflex is more deep-seated in the organism, and more essential to
its welfare. The reflex is typically quicker than the simple reaction.
The reflex machinery does not need a "Ready" signal, nor any
preparation, but is always ready for business. (The subject in a
simple reaction experiment would not make the particular finger
movement that he makes unless he had made ready for that movement.)
The attachment of a certain response to a certain stimulus, rather
arbitrary and temporary in the simple reaction, is inherent and
permanent in the reflex. Reflex action is involuntary and often
entirely unconscious.
Reflexes, we said, are permanent. That is because they {26} are native
or inherent in the organism. You can observe them in the new-born
child. The reflex connection between stimulus and response is
something the child brings with him into the world, as distinguished
from what he has to acquire through training and experience. He does
acquire, as he grows up, a tremendous number of habitual responds that
become automatic and almost unconscious, and these "secondary
automatic" reactions resemble reflexes pretty closely. Grasping for
your hat when you feel the wind taking it from your head is an
example. These acquired reactions never reach the extreme speed of the
quickest reflexes, but at best may have about the speed of the simple
reaction. Though often useful enough, they are not so fundamentally
necessary as the reflexes. The reflex connection of stimulus and
response is something essential, native, closely knit, and always
ready for action.
The Nerves in Reflex Action
Seeing that the response, in reflex action, is usually made by a
muscle or gland lying at some distance from the sense organ that
receives the stimulus--as, in the case of the flexion reflex, the
stimulus is applied to the skin of the hand (or foot), while the
response is made by muscles of the limb generally--we have to ask what
sort of connection exists between the stimulated organ and the
responding organ, and we turn to physiology and anatomy for our
answer. The answer is that the _nerves_ provide the connection. Strands
of nerve extend from the sense organ to the muscle.
But the surprising fact is that the nerves do not run directly from
the one to the other. There is no instance in the human body of a
direct connection between any sense organ and any muscle or gland. The
nerve path from sense organ to muscle always leads through a _nerve
center_. One {27} nerve, called the sensory nerve, runs from the sense
organ to the nerve center, and another, the motor nerve, runs from the
center to the muscle; and the only connection between the sense organ
and the muscle is this roundabout path through the nerve center. The
path consists of three parts, sensory nerve, center, and motor nerve,
but, taken as a whole, it is called the _reflex arc_, both the words,
"reflex" and "arc", being suggested by the indirectness of the
connection.
[Illustration: Fig. 1.--The connection from the back of the hand,
which is receiving a stimulus, and the arm muscle which makes the
response. The nerve center is indicated by the dotted lines.]
The _nervous system_ resembles a city telephone system. What passes
along the nerve is akin to the electricity that {28} passes along the
telephone wire; it is called the "nerve current", and is electrical
and chemical in nature.
[Illustration: Fig. 2.--(From Martin's "Human Body.") General view of
the nervous system, showing brain, cord, and nerves.]
All nerve connections, like the great majority of telephone
connections, are effected through the centers, called "centrals" in
{29} the case of the telephone. Telephone A is connected directly with
the central, telephone B likewise, and A and B are indirectly
connected, through the central switchboard. That is the way it is in
the nervous system, with "nerve center" substituted for "central", and
"sense organ" and "muscle or gland" for "telephones A and B."
[Illustration: Fig. 3.--Location of the cord, cerebrum and cerebellum.
The brain stem continues the cord upward into the skull cavity.
(Figure text: cerebrum, cerebellum, cord, tongue)]
The advantage of the centralized system is that it is a _system_,
affording connections between any part and any other, and unifying the
whole complex organism.
The _nerve centers_ are located in the brain and spinal cord. The
brain lies in the skull and the cord extends from the brain down
through a tube in the middle of the {30} backbone. Of the brain many
parts can be named, but for the present it is enough to divide it into
the "brain stem", a continuation of the spinal cord up along the base
of the skull cavity, and the two great outgrowths of the brain stem,
called "cerebrum" and "cerebellum". The spinal cord and brain stem
contain the lower or reflex centers, while the cerebellum, and
especially the cerebrum, contain the "higher centers". The lower
centers are directly connected by nerves with the sense organs, glands
and muscles, while the higher centers have direct connections with the
lower and only through them with the sense organs, glands and muscles.
In other words, the sensory nerves run into the cord or brain stem,
and the motor nerves run out of these same, while interconnecting
nerve strands extend between the lower centers in the cord and brain
stem and the higher centers in the cerebrum and cerebellum.
The spinal cord contains the reflex centers for the limbs and part of
the trunk, and is connected by sensory and motor nerves with the limbs
and trunk. The brain stem contains the reflex centers for the head and
also for part of the interior of the trunk, including the heart and
lungs, and is connected with them by sensory and motor nerves. The
nerve center that takes part in the flexion reflex of the foot is
situated in the lower part of the cord, that for the similar reflex of
the hand lies in the upper part of the cord, that for breathing lies
in the lower or rear part of the brain stem, and that for winking lies
further forward in the brain stem.
Big movements, such as the combined action of all four legs of an
animal in walking, require cord and brain stem to work together, and
throw into relief what is really true even of simpler reflexes, namely
that a reflex is a _coordinated_ movement, in the sense that different
muscles cooperate in its execution.
{31}
Internal Construction of the Nerves and Nerve Centers
We shall understand nerve action better if we know something of the
way in which the nervous system is built. A nerve is not to be thought
of as a unit, nor are the brain and cord to be thought of as mere
masses of some peculiar substance.
[Illustration: Fig. 4.--A motor nerve cell from the spinal cord,
highly magnified. (Figure text: dendrites, cell body, axon,
termination of axon in muscle)]
A nerve is a bundle of many slender insulated threads, just as a
telephone cable, running along the street, {32} is a bundle of many
separate wires which are the real units of telephonic communication. A
nerve center, like the switchboard in a telephone central, consists of
many parts and connections.
The whole nervous system is essentially composed of _neurones_. A
neurone is a nerve cell with its branches. Most nerve cells have two
kinds of branches, called the _axon_ and the _dendrites_.
The nerve cell is a microscopic speck of living matter. Its dendrites
are short tree-like branches, while its axon is often several inches
or even feet in length. The axon is the "slender thread", just spoken
of as analogous to the single telephone wire. A nerve is composed of
axons. [Footnote: The axon is always protected or insulated by a
sheath, and axon and sheath, taken together, are often called a "nerve
fiber".] The "white matter" of the brain and cord is composed of
axons. Axons afford the means of communication between the nerve
centers and the muscles and sense organs, and between one nerve center
and another.
The axons which make up the motor nerves are branches of nerve cells
situated in the cord and brain stem; they extend from the reflex
center for any muscle out to and into that muscle and make very close
connection with the muscle substance. A nerve current, starting from
the nerve cells in the reflex center, runs rapidly along the axons to
the muscle and arouses it to activity.
The axons which make up the optic nerve, or nerve of sight, are
branches of nerve cells in the eye, and extend into the brain stem.
Light striking the eye starts nerve currents, which run along these
axons into the brain stem. Similarly, the axons of the nerve of smell
are branches of cells in the nose.
The remainder of the sensory axons are branches of nerve cells that
lie in little bunches close alongside the cord or {33} brain stem.
These cells have no dendrites, but their axon, dividing, reaches in
one direction out to a sense organ and in the other direction into the
cord or brain stem, and thus connects the sense organ with its "lower
center".
[Illustration: Fig. 5.--Sensory and motor axons, and their nerve
cells. The arrows indicate the direction of conduction. (Figure text:
eye, brain stem, skin, cord, muscle)]
Where an axon terminates, it broadens out into a thin plate, or breaks
up into a tuft of very fine branches ( the "end-brush"), and by this
means makes close contact with the muscle, the sense organ, or the
neurone with which it connects.
{34}
The Synapse
Now let us consider the mode of connection between one neurone and
another in a nerve center. The axon of one neurone, through its
end-brush, is in close contact with the dendrites of another neurone.
There is contact, but no actual growing-together; the two neurones
remain distinct, and this contact or junction of two neurones is
called a "synapse". The synapse, then, is not a thing, but simply a
junction between two neurones.
[Illustration: Fig. 6.--The synapse between the two neurones lies just
above the arrow.]
The junction is good enough so that one of the two neurones, if itself
active, can arouse the other to activity. The end-brush, when a nerve
current reaches it from its own nerve cell, arouses the dendrites of
the other neurone, and thus starts a nerve current running along those
dendrites to their nerve cell and thence out along its axon.
Now here is a curious and significant fact: the dendrites are
receiving organs, not transmitting; they pick up messages from the
end-brushes across the synapse, but send out no messages to those
end-brushes. Communication across a synapse is always in one
direction, from end-brush to dendrites.
This, then, is the way in which a reflex is carried out, the pupillary
reflex, for example. Light entering the eye starts a nerve current in
the axons of the optic nerve; these axons terminate in the brain stem,
where their end-brushes arouse the dendrites of motor nerve cells, and
the axons of these {35} cells, extending out to the muscle of the
pupil, cause it to contract, and narrow the pupil.
Or again, this is the way in which one nerve center arouses another to
activity. The axons of the cells in the first center (or some of them)
extend out of this center and through the white matter to the second
center, where they terminate, their end-brushes forming synapses with
the cells of the second center. Let the first center be thrown into
activity, and immediately, through this connection, it arouses the
second.
[Illustration: Fig. 7.--Different forms of synapse found in the
cerebellum, "a" is one of the large motor cells of the cerebellum (a
"Purkinje cell"), with its dendrites above and its axon below; and
"b," "c" and "d" show three forms of synapse made by other neurones
with this Purkinje cell. In "b," the arrow indicates a "climbing
axon," winding about the main limbs of the Purkinje cell. In "c," the
arrow points to a "basket"--an end-brush enveloping the cell body;
while "d" shows what might be called a "telegraph-wire synapse."
Imagine "d" superimposed upon "a": the axon of "d" rises among the
fine dendrites of "a," and then runs horizontally through them; and
there are many, many such axons strung among the dendrites. Thus the
Purkinje cell is stimulated at three points: cell body, trunks of the
dendrites, and twigs of the dendrites.]
The "gray matter" comprises the nerve centers, lower and higher. It is
made up of nerve cells and their dendrites, of the beginnings of axons
issuing from these cells and of the terminations of incoming axons.
The white matter, as was said before, consists of axons. An axon
issues from the {36} gray matter at one point, traverses the white
matter for a longer or shorter distance, and finally turns into the
gray matter at another point, and thus nerve connection is maintained
between these two points.
There are lots of nerve cells, billions of them. That ought to be
plenty, and yet--well, perhaps sometimes they are not well developed,
or their synapses are not close enough to make good connections.
[Illustration: Fig. 8.--A two-neurone reflex arc. (Figure text:
stimulus, skin, sensory axon, bit of the spinal cord, motor axon,
muscle)]
Examined under the microscope, the nerve cell is seen to contain,
besides the "nucleus" which is present in every living cell and is
essential for maintaining its vitality and special characteristics,
certain peculiar granules which appear to be stores of fuel to be
consumed in the activity of the cell, and numerous very fine fibrils
coursing through the cell and out into the axon and dendrites.
The _reflex arc can now be described_ more precisely than before.
Beginning in a sense organ, it extends along a sensory axon (really
along a team of axons acting side by side) to its end-brush in a lower
center, where it crosses a synapse and enters the dendrites of a motor
neurone and so {37} reaches the cell body and axon of this neurone,
which last extends out to the muscle (or gland). The simplest reflex
arc consists then of a sensory neurone and a motor neurone, meeting at
a synapse in a lower or reflex center. This would be a two-neurone
arc.
[Illustration: Fig. 9.--A three-neurone arc, concerned in respiration.
This also illustrates how one nerve center influences another.
(Figure text: white matter, gray matter, lung, respiratory center in
the brain stem, diaphragm, motor center in cord for the diaphragm)]
Very often, and possibly always, the reflex arc really consists of
three neurones, a "central" neurone intervening between the sensory
and motor neurones and being connected through synapses with each. The
central neurone plays an important rôle in coördination.
COÖRDINATION
The internal structure of nerve centers helps us see how coördinated
movement is produced. The question is, how {38} several muscles are
made to work together harmoniously, and also how it is possible that a
pin prick, directly affecting just a few sensory axons, causes a big
movement of many muscles. Well, we find the sensory axon, as it enters
the cord, sending off a number of side branches, each of which
terminates in an end-brush in synaptic connection with the dendrites
of a motor nerve cell.
[Illustration: Fig. 10.--Coördination brought about by the branching
of a sensory axon. (Figure text: cord, sensory neurone, motor neurone)]
Thus the nerve current from a single sensory neurone is distributed to
quite a number of motor neurones. Where there are central neurones in
the arc, their branching axons aid in distributing the excitation; and
so we get a big movement in response to a minute, though intense
stimulus.
But the response is not simply big; it is definite, coordinated,
representing team work on the part of the muscles as distinguished
from indiscriminate mass action. That means selective distribution of
the nerve current. The axons of the sensory and central neurones do
not connect with any and every motor neurone indiscriminately, but
link up with selected groups of motor neurones, and thus harness
together teams that will work in definite ways, producing {39} flexion
of a limb in the case of one such team, and extension in the case of
another. Every reflex has its own team of motor neurones, harnessed
together by its outfit of sensory and central neurones. The same motor
neurone may however be harnessed into two or more such teams, as is
seen from the fact that the same muscle may participate in different
reflex movements; and for a similar reason we believe that the same
sensory neurone may be utilized in more than one reflex arc.
[Illustration: Fig. 11.--Coördination brought about by the branching
of the axon of a central neurone. (Figure text: sensory, central,
motor)]
The most distinctive part of any reflex arc is likely to be its
central neurones, which are believed to play the chief part in
coördination, and in determining the peculiarities of any given
reflex, such as its speed and rhythm of action.
Reactions in General
Though the reflex is simple by comparison with voluntary movements, it
is not the simplest animal reaction, for it is coördinated and depends
on the nervous system, while the simplest animals, one-celled animals,
have no nervous system, any more than they have muscles or organs of
any {40} kind. Without possessing separate organs for the different
vital functions, these little creatures do nevertheless take in and
digest food, reproduce their kind, and move. Every animal shows at
least two different motor reactions, a positive or approaching
reaction, and a negative or avoiding reaction.
The general notion of a reaction is that of a _response_ to a
_stimulus_. The stimulus acts on the organism and the organism acts
back. If I am struck by a wave and rolled over on the beach, that is
passive motion and not my reaction; but if the wave stimulates me to
maintain my footing, then I am active, I respond or react.
Now there is no such thing as wholly passive motion. Did not Newton
teach that "action and reaction are equal"?--and he was thinking of
stones and other inanimate objects. The motion of a stone or ball
depends on its own weight and shape and elasticity as much as on the
blow it receives. Even the stone counts for something in determining
its own behavior.
A loaded gun counts for more than a stone, because of the stored
energy of the powder that is set free by the blow of the hammer. The
"reaction" of the gun is greater than the force acting on it, because
of this stored energy that is discharged.
An animal reaction resembles the discharge of the gun, since there is
stored energy in the animal, consisting in the chemical attraction
between food absorbed and oxygen inspired, and some of this energy is
utilized and converted into motion when the animal reacts. The
stimulus, like the trigger of the gun, simply releases this stored
energy.
The organism, animal or human, fully obeys the law of conservation of
energy, all the energy it puts out being accounted for by stored
energy it has taken in in food and oxygen. But at any one time, when
the organism receives {41} a stimulus, the energy that it puts forth
in reaction comes from inside itself.
There is another way in which the organism counts in determining its
reaction. Not only does it supply the energy of the response, but its
own internal arrangements determine how that energy shall be directed.
That is to say, the organism does not blow up indiscriminately, like a
charge of dynamite, but makes some definite movement. This is true
even of the simplest animals, and the more elaborate the internal
mechanism of the animal, the more the animal itself has to do with the
kind of response it shall make to a stimulus. The nervous system of
the higher animals, by the connections it provides between the
stimulus and the stores of energy in the muscles, is of especial
importance in determining the nature of the response.
Stimuli are necessary to arouse the activity of the organism. Without
any stimulus whatever, it seems likely that the animal would relapse
into total inactivity. It should be said, however, that stimuli, such
as that of hunger, may arise within the organism itself. The stimulus
may be external or internal, but some stimulus is necessary in order
to release the stored energy.
In general, then, a reaction consists in the release by a stimulus of
some of the stored energy of an animal, and the direction of that
energy by the animal's own internal mechanism of nerves and muscles
(and, we may add, bones and sinews) into the form of some definite
response.
{42}
EXERCISES
1. Outline of the chapter, being at the same time a "completion
test". Complete the following outline by filling in the blank
spaces (usually a single word will fill the blank, but sometimes two
words will be better):
A. Definition: A reaction is a response to a ___________.
The stimulus energy stored in the organism, and the __________
has a definite form determined by the organism's own machinery
of ________ and ______.
B. Among very prompt reactions are the reflex and the "simple
reaction". The reflex differs from the "simple reaction" in that:
(1) It usually takes less________.
(2) It requires no___________,
(3) The machinery for it is ________in the organism.
C. The machinery for a reflex consists of:
(1) a________ organ.
(2) a ________nerve.
(3) a nerve ________,
(4) a _________nerve.
(5) a muscle or _________.
D. The sensory and motor nerves consist of ________ which are
branches of ______. The cells for the motor nerves lie in the
________, and those for the sensory nerves lie in two cases in
the _________, and in all other cases in bunches located close
beside the _________or ________,
E. The neurone is the _______ of which the nervous ______ is
composed. It consists of a ________ and of two sorts of
branches, the ________ and the ________. Internally, the neurone
shows a peculiar structure of ________ and ________.
F. Communication from one neurone to another occurs across
a _____ called the synapse. The _________of an axon here comes
into close contact with the ______or with the _________of
another neurone. The communication takes place from the
________of the first neurone to the ___________ of the second.
G. The "nerve current" in a reflex therefore runs the following
course: from the sense organ into a ________ axon, along this to
its _________ in a nerve, and across a _________ there into the
_________ of a neurone, and thence {43} out along the _______of
this neurone to the ________or _________ that executes the
reflex. This is a two-neurone _________, but often there is a
third, ________neurone between the _________ and the
_____________.
H. Coördination is effected by the ________ of the axons of the
sensory and ________ neurones, by which means the nerve current
is ______ to a team of ________ and so to a team of _________.
2. Is the reaction time experiment, as described in the text, an
introspective or an objective experiment?
3. Mention two cases from common life that belong under the
"simple reaction", two that belong under "choice reaction", and two
that belong under the "associative reaction".
4. Arrange the reflexes mentioned in the text under the two heads
of "protective" and "regulative".
5. Draw diagrams of (a) the neurone, (b) a synapse, (c) a reflex
arc, and (d) a coördinated movement. Reduce each drawing to the
simplest possible form, and still retain everything that is
essential.
6. What part of the nervous system lies (a) in the forehead and
top of the head, (b) in the very back of the head, (c) along the
base of the skull, (d) within the backbone, (e) in the arm?
7. Using a watch to take the time, see how long it takes you to
name the letters in a line of print, reading them in reverse order
from the end of the line to the beginning. Compare with this time
the time required to respond to each letter by the letter following
it in the alphabet (saying "n" when you see m, and "t" when you see
s, etc.). Which of these two "stunts" is more like reflex action,
and how, nevertheless, does it differ from true reflex action?
8. The pupillary reflex. Describe the reaction of the pupil of the
eye to light suddenly shining into the eye. This response can best
be observed in another person, but you can observe it in yourself
by aid of a hand mirror. On another person you can also observe the
"crossed" pupillary reflex, by throwing the light into one eye only
while you watch the other eye. What sort of connection do you
suppose to exist between the two eyes, making this crossed reflex
possible?
9. The lid reflex, or wink reflex, (a) Bring your hand suddenly
close to another person's eye, and notice the response of the
eyelid, (b) See whether you can get a crossed reflex here, (c) See
whether your subject can voluntarily prevent (inhibit) the lid
reflex, (d) See whether the reflex occurs when he gives the
stimulus himself, by moving his own hand suddenly up to his eye.
(e) What other stimulus, besides the visual one that you have been
using, will arouse the same response?
{44}
REFERENCES
C. Judson Herrick, in his _Introduction to Neurology_, 2nd edition,
1918, gives a fuller and yet not too detailed account of the neurone
in Chapter III, and of reflex action in Chapter IV.
Percy G. Stiles, in his _Nervous System and Its Conservation_, 1915,
discusses these matters in Chapters II, III and IV.
Ladd and Woodworth's _Elements of Physiological Psychology_, 1911, has
chapters on these topics.
{45}
CHAPTER III
REACTIONS OF DIFFERENT LEVELS
HOW SENSATIONS, PERCEPTIONS AND THOUGHTS MAY BE CONSIDERED AS FORMS OF
INNER RESPONSE, AND HOW THESE HIGHER REACTIONS ARE RELATED IN THE
NERVOUS SYSTEM TO THE SIMPLER RESPONSES OF THE REFLEX LEVEL.
Having defined a reaction as an act of the individual aroused by a
stimulus, there is no reason why we should not include a great variety
of mental processes under the general head of reactions. Any mental
process is an activity of the organism, and it is aroused by some
stimulus, external or internal; therefore, it is a reaction.
I hear a noise--now, while the noise, as a physical stimulus, comes to
me, my hearing it is my own act, my sensory reaction to the stimulus.
I recognize the noise as the whistle of a steamboat--this recognition
is clearly my own doing, dependent on my own past experience, and may
be called a perception or perceptive response. The boat's whistle
reminds me of a vacation spent on an island--clearly a memory
response. The memory arouses an agreeable feeling--an affective
response, this may be called. In its turn, this may lead me to imagine
how pleasant it would be to spend another vacation on that island, and
to cast about for ways and means to accomplish this result--here we
have imagination and reasoning, aroused by what preceded just as the
sensation was aroused by the physical stimulus.
In speaking of any mental process as an act of the individual, we do
not mean to imply that he is always _conscious_ {46} of his activity.
Sometimes he feels active, sometimes passive. He feels active in hard
muscular work or hard thinking, while he feels passive in reflex
action, in sensation, and in simply "being reminded" of anything
without any effort on his own part. But he is active in everything he
does, and he does everything that depends on his being alive. Life is
activity, and every manifestation of life, such as reflex action or
sensation, is a form of vital activity. The only way to be inactive is
to be dead.
But vital activity is not "self-activity" in any absolute sense, for
it is _aroused_ by some stimulus. It does not issue from the
individual as an isolated unit, but is his _response_ to a stimulus.
That is the sense of calling any mental process a reaction; it is
something the individual does in response to a stimulus.
To call a sensation a form of reaction means, then, that the sensation
is not something done to the person, nor passively received by him
from outside, but something that he himself does when aroused to this
particular form of activity. What comes from outside and is received
by the individual is the stimulus, and the sensation is what he does
in response to the stimulus. It represents the discharge of internal
stored energy in a direction determined by his own inner mechanism.
The sensation depends on his own make-up as well as on the nature of
the stimulus, as is especially obvious when the sensation is abnormal
or peculiar. Take the case of color blindness. The same stimulus that
arouses in most people the sensation of red arouses in the color-blind
individual the sensation of brown. Now what the color-blind individual
_receives_, the light stimulus, is the same as what others receive,
but he responds differently, _i.e._, with a different sensation,
because his own sensory apparatus is peculiar.
The main point of this discussion is that all mental {47} phenomena,
whether movements, sensations, emotions, impulses or thoughts, are a
person's acts, but that every act is a response to some present
stimulus. This rather obvious truth has not always seemed obvious.
Some theorists, in emphasizing the spontaneity and "self-activity" of
the individual, have pushed the stimulus away into the background;
while others, fixing their attention on the stimulus, have treated the
individual as the passive recipient of sensation and "experience"
generally. Experience, however, is not received; it is lived, and that
means done; only, it is done in response to stimuli. The concept of
reaction covers the ground.
While speaking of sensations and thoughts as belonging under the
general head of reactions, it is well, however, to bear in mind that
all mental action tends to arouse and terminate in muscular and
glandular activity. A thought or a feeling tends to "express itself"
in words or (other) deeds. The motor response may be delayed, or
inhibited altogether, but the tendency is always in that direction.
Different Sorts of Stimuli
To call all mental processes reactions means that it is always in
order to ask for the stimulus. Typically, the stimulus is an external
force or motion, such as light or sound, striking on a sense organ.
There are also the internal stimuli, consisting of changes occurring
within the body and acting on the sensory nerves that are distributed
to the muscles, bones, lungs, stomach and most of the organs. The
sensations of muscular strain and fatigue, and of hunger and thirst,
are aroused by internal stimuli, and many reflexes are aroused in the
same way.
Such internal stimuli as these are like the better known external
stimuli in that they act upon sense organs; but it {48} seems
necessary to recognize another sort of stimuli which act directly on
the nerve centers in the brain. These may be called "central stimuli"
and so contrasted with the "peripheral stimuli" that act on any sense
organ, external or internal. To do this is to take considerable
liberty with the plain meaning of "stimulus", and calls for
justification. What is the excuse for thus expanding the notion of a
stimulus?
The excuse is found in the frequent occurrence of mental processes
that are not directly aroused by any peripheral stimulus, though they
are plainly aroused by something else. Anything that arouses a thought
or feeling can properly be called its stimulus. Now it often happens
that a thought is aroused by another, just preceding thought; and it
seems quite in order to call the first thought the stimulus and the
second the response. A thought may arouse an emotion, as when the
thought of my enemy, suddenly occurring to mind, makes me angry; the
thought is then the stimulus arousing this emotional response.
If hearing you speak of Calcutta makes me think of India, your words
are the stimulus and my thought the response. Well, then, if I _think_
of Calcutta in the course of a train of thought, and next think of
India, what else can we say than that the thought of Calcutta acts as
a stimulus to arouse the thought of India as the response? In a long
train of thought, where A reminds you of B and B of C and C of D, each
of these items is, first, a response to the preceding, and, second, a
stimulus to the one following.
There is no special difficulty with the notion of "central stimuli"
from the physiological side. We have simply to think of one nerve
center arousing another by means of the tract of axons connecting the
two. Say the auditory center is aroused by hearing some one mention
your friend's name, {49} and this promptly calls up a mental picture
of your friend; here the auditory center has aroused the visual. What
happens in a train of thought is that first one group of neurones is
aroused to activity, and then this activity, spreading along the axons
that extend from this group of neurones to another, arouses the second
group to activity; and so on. The brain process may often be
exceedingly complex, but this simple scheme gives the gist of it.
The way nerve currents must go shooting around the brain from one
center or group of neurones to another, keeping it up for a long time
without requiring any fresh peripheral stimulus, is remarkable. We
have evidence of this sort of thing in a dream or fit of abstraction.
Likely enough, the series of brain responses would peter out after
awhile, in the absence of any fresh peripheral stimulus, and total
inactivity ensue. But response of one brain center to nerve currents
coming from another brain center, and not directly from any sense
organ, must be the rule rather than the exception, since most of the
brain neurones are not directly connected with any sense organ, but
only with other parts of the brain itself. All the evidence we have
would indicate that the brain is not "self-active", but only
responsive; but, once thrown into activity at one point, it may
successively become active at many other points, so that a long series
of mental operations may follow upon a single sensory stimulus.
The Motor Centers, Lower and Higher
A "center" is a collection of nerve cells, located somewhere in the
brain or cord, which gives off axons running to some other center or
out to muscles or glands, while it also receives axons coming from
other centers, or from sense organs. These incoming axons terminate in
end-brushes and so form synapses with the dendrites of the local {50}
nerve cells. The axons entering any center and terminating there
arouse that center to activity, and this activity, when aroused, is
transmitted out along the axons issuing from that center, and produces
results where those axons terminate in their turn.
[Illustration: Fig. 12.--Side view of the left hemisphere of the
brain, showing the motor and sensory areas (for the olfactory area,
see Fig. 18). The visual area proper, or "visuo-sensory area," lies
just around the corner from the spot marked "Visual," on the middle
surface of the hemisphere, where it adjoins the other hemisphere.
(Figure text: frontal lobe, parietal lobe, central fissure, occipital
lobe, motor area, somesthetic area, auditory area, fissure of Sylvius,
temporal lobe, brain stem, cerebellum)]
The _lower_ motor centers, called also reflex centers, are located in
the cord or brain stem, and their nerve cells give rise to the axons
that form the motor nerves and connect with the muscles and glands. A
muscle is thrown into action by nerve currents from its lower motor
center.
The principal _higher_ motor center is the "motor area" of the brain,
located in the cortex or external layer of gray matter, in the
cerebrum. More precisely, the motor area is a long, narrow strip of
cortex, lying just forward of what is called the "central fissure" or
"fissure of Rolando".
{51}
If you run your finger over the top of the head from one side to the
other, about halfway back from the forehead, the motor areas of the
two cerebral hemispheres will lie close under the path traced by your
finger.
[Illustration: Fig. 13.--(After Cajal.) Type of the brain cells that
most directly control muscular movement. (Figure text: Axon. Giant
pyramid cell from the motor area of the cerebral cortex, magnified 35
diameters. Cell body of same farther magnified)]
The motor area in the right hemisphere is connected with the left half
of the cord and so with the muscles of the left half of the body; the
motor area of the left hemisphere similarly affects {52} the right
half of the body. Within the motor area are centers for the several
limbs and other motor organs. Thus, at the top, near the middle line
of the head (and just about where the phrenologists located their
"bump of veneration"!), is the center for the legs; next below and to
the side is the center for the trunk, next that for the arm, next that
for head movements, and at the bottom, not far from the ears, is the
center for tongue and mouth.
[Illustration: Fig. 14.--The nerve path by which the motor area of the
cortex influences the muscles. The upper part of this path, consisting
of axons issuing from the giant pyramids of the motor area and
extending down into the spinal cord, is the pyramidal tract. The lower
part of the path consists of axons issuing from the motor cells of the
cord and extending out to the muscles. The top of the figure
represents a vertical cross-section of the brain, such as is given, on
a larger scale, in Fig. 18. (Figure text: cortex, cord, muscles)]
The largest nerve cells of all are found in the motor area, and are
called, from their shape, the "giant pyramids". They have large
dendrites and very long axons, which latter, {53} running in a thick
bundle down from the cortex through the brain stem and cord,
constitute the "pyramidal tract", the principal path of communication
from the cerebrum to the lower centers. The motor area of the brain
has no direct connection with any muscle, but acts through the
pyramidal tract on the lower centers, which in turn act on the
muscles.
How The Brain Produces Muscular Movements
The motor area is itself aroused to action by nerve currents entering
it through axons coming from other parts of the cortex; and it is by
way of the motor area that any other part of the cortex produces
bodily movement. There are a few exceptions, as, for example, the
movements of the eyes are produced generally by the "visual area"
acting directly on the lower motor centers for the eye in the brain
stem; but, in the main, any motor effect of brain action is exerted
through the motor area. The motor area, as already mentioned, acts on
the lower motor centers in the cord and brain stem, and these in turn
on the muscles; but we must look into this matter a little more
closely.
A lower motor center is a group of motor and central neurones, lying
anywhere in the cord or brain stem, and capable of directly arousing a
certain coördinated muscular movement. One such unit gives flexion of
the leg, another gives extension of the leg, a third gives the rapid
alternation of flexion and extension that we see in the scratching
movement of the dog. Such a motor center can be aroused to activity by
a sensory stimulus, and the resulting movement is then called a
reflex.
The lower center can be aroused in quite another way, and that is by
nerve currents coming from the brain, by way of the motor area and the
pyramidal tract. Thus flexion of the leg can occur voluntarily as well
as reflexly. The same {54} muscles, and the same motor neurones, do
the job in either case. In the reflex, the lower center is aroused by
a sensory nerve, and in the voluntary movement by the pyramidal tract.
The story is told of a stranger who was once dangling his legs over
the edge of the station platform at a small backwoods town, when a
native called out to him "Hist!" (hoist), pointing to the ground under
the stranger's feet. He "histed" obediently, which is to say that he
voluntarily threw into play the spinal center for leg flexion; and
then, looking down, saw a rattler coiled just beneath where his feet
had been hanging. Now even if he had spied the rattler first, the
resulting flexion, though impulsive and involuntary, would still have
been aroused by way of the motor area and the pyramidal tract, since
the movement would have been a response to _knowledge_ of what that
object was and signified, and knowledge means action by the cerebral
cortex, which we have seen to affect movement through the medium of
the motor area. But if the snake had made the first move, the same leg
movement on the man's part, made now in response to the painful
sensory stimulus, would have been the flexion reflex.
Facilitation and Inhibition
Not only can the motor area call out essentially the same movements
that are also produced reflexly, but it can prevent or _inhibit_ the
execution of a reflex in spite of the sensory stimulus for the reflex
being present, and it can reinforce or _facilitate_ the action of the
sensory stimulus so as to assist in the production of the reflex. We
see excellent examples of cerebral facilitation and inhibition in the
case of the knee jerk. This sharp forward kick of the foot and lower
leg is aroused by a tap on the tendon running in front {55} of the
knee. Cross the knee to be stimulated over the other leg, and tap the
tendon just below the knee cap, and the knee jerk appears. So purely
reflex is this movement that it cannot be duplicated voluntarily; for,
though the foot can of course be voluntarily kicked forward, this
voluntary movement does not have the suddenness and quickness of the
true reflex. For all that, the cerebrum can exert an influence on the
knee jerk. Anxious attention to the knee jerk inhibits it; gritting
the teeth or clenching the fist reinforces it. These are cerebral
influences acting by way of the pyramidal tract upon the spinal center
for the reflex.
Thus the cortex controls the reflexes. Other examples of such control
are seen when you prevent for a time the natural regular winking of
the eyes by voluntarily holding them wide open, or when, carrying a
hot dish which you know you must not drop, you check the flexion
reflex which would naturally pull the hand away from the painful
stimulus. The young child learns to control the reflexes of
evacuation, and gradually comes to have control over the breathing
movements, so as to hold his breath or breathe rapidly or deeply at
will, and to expire vigorously in order to blow out a match.
The coughing, sneezing and swallowing reflexes likewise come under
voluntary control. In all such cases, the motor area facilitates or
inhibits the action of the lower centers.
Super-motor Centers in the Cortex
Another important effect of the motor area upon the lower centers
consists in combining their action so as to produce what we know as
skilled movements. It will be remembered that the lower centers
themselves give coördinated movements, such as flexion or extension of
the whole limb; but still higher coördinations result from cerebral
control. {56} When the two hands, though executing different
movements, work together to produce a definite result, we have
coördination controlled by the cortex. Examples of this are seen in
handling an ax or bat, or in playing the piano or violin. A movement
of a single hand, as in writing or buttoning a coat, may also
represent a higher or cortical coördination.
[Illustration: Fig. 15.--(From Starr.) Axons connecting one part of
the cortex with another. The brain is seen from the side, as if in
section. At "A" are shown bundles of comparatively short axons,
connecting near-by portions of the cortex; while "B," "C," and "D"
show bundles of longer axons, connecting distant parts of the cortex
with one another. The "Corpus Callosum" is a great mass of axons
extending across from each cerebral hemisphere to the other, and
enabling both hemispheres to work together. "O. T." and "C. N." are
interior masses of gray matter, which can be seen also in Fig. 18. "O.
T." is the thalamus, about which more later.]
Now it appears that the essential work in producing these higher
coördinations of skilled movement is performed not by the motor area,
but by neighboring parts of the cortex, which act on the motor area in
much the same way as the motor area acts on the lower centers. Some of
these {57} skilled-movement centers, or super-motor centers, are
located in the cortex just forward of the motor area, in the adjacent
parts of the frontal lobe. Destruction of the cortex there, through
injury or disease, deprives the individual of some of his skilled
movements, though not really paralyzing him. He can still make simple
movements, but not the complex movements of writing or handling an
instrument.
It is a curious fact that the left hemisphere, which exerts control
over the movements of the right hand and right side of the body
generally, also plays the leading part in skilled movements of either
hand. This is true, at least, of right-handed persons; probably in the
left-handed the right hemisphere dominates.
Motor power may be lost through injury at various points in the
nervous system. Injury to the spinal cord, destroying the lower motor
center for the legs, brings complete paralysis. Injury to the motor
area or to the pyramidal tract does not destroy reflex movement, but
cuts off all voluntary movement and cerebral control. Injury to the
"super-motor centers" causes loss of skilled movement, and produces the
condition of "apraxia", in which the subject, though knowing what he
wants to do, and though still able to move his limbs, simply cannot
get the combination for the skilled act that he has in mind.
Speech Centers
Similar to apraxia is "aphasia" or loss of ability to speak. It bears
the same relation to true paralysis of the speech organs that hand
apraxia bears to paralysis of the hand. Through brain injury it
sometimes happens that a person loses his ability to speak words,
though he can still make vocal sounds. The cases differ in severity,
some retaining the ability to speak only one or two words which {58}
from frequent use have become almost reflex (swear words, sometimes,
or "yes" and "no"), while others are able to pronounce single words,
but can no longer put them together fluently into the customary form
of phrases and sentences, and still others can utter simple sentences,
but not any connected speech.
[Illustration: Fig. 16.--Side view of the left hemisphere, showing the
location of the "speech centers." The region marked "Motor" is the
motor speech center, that marked "Auditory" the auditory speech
center, and that marked "Visual" the visual speech center. (Figure text:
central fissure, motor area, auditory area, visual area, fissure of
Sylvius, brain stem, cerebellum)]
In pure cases of _motor aphasia_, the subject knows the words he
wishes to say, but cannot get them out. The brain injury here lies in
the frontal lobe in the left hemisphere, in right-handed people, just
forward of the motor area for the mouth, tongue and larynx. This
"motor speech center" is the best-known instance of a super-motor
center. It coördinates the elementary speech movements into the
combinations called words; and perhaps there is no other motor
performance so highly skilled as this of speaking. It is acquired so
early in life, and practised so constantly, that {59} we take it quite
as a matter of course, and think of a word as a simple and single
movement, while in fact even a short word, as spoken, is a complex
movement requiring great motor skill.
There is some evidence that the motor speech center extends well
forward into the frontal lobe, and that the front part of it is
related to the part further back as this is to the motor area back of
it. That is to say, the back of the speech center combines the motor
units of the motor area into the skilled movements of speaking a word,
while the more forward part of the speech center combines the word
movements into the still more complex movement of speaking a sentence.
It is even possible that the very front part of the speech center has
to do with those still higher combinations of speech movements that
give fluency and real excellence of speaking.
The Auditory Centers
Besides the motor aphasia, just mentioned, there is another type,
called _sensory aphasia_, or, more precisely, auditory aphasia. In
pure auditory aphasia there is no inability to pronounce words or even
to speak fluently, but there is, first, an inability to "hear words",
sometimes called word deafness, and there is often also an inability
to find the right words to speak, so that the individual so afflicted,
while speaking fluently enough and having sense in mind, misuses his
words and utters a perfect jargon. One old gentleman mystified his
friends one morning by declaring that he must go and "have his
umbrella washed", till it was finally discovered that what he wanted
was to have his hair cut.
The cortical area affected in this form of aphasia is located a little
further back on the surface of the brain than {60} the motor speech
center, being close to the auditory area proper. The latter is a small
cortical region in the temporal lobe, connected (through lower
centers) with the ear, and is the only part of the cortex to receive
nerve currents from the organ of hearing. The auditory area is,
indeed, the organ of hearing, or an organ of hearing, for without it
the individual is deaf. He may make a few reflex responses to loud
noises, but, consciously, he does not hear at all; he has no auditory
sensations.
In the immediate neighborhood of the auditory area proper (or of the
"auditory-sensory area", as it may well be called), are portions of
the cortex intimately connected by axons with it, and concerned in
what may be called auditory perceptions, i.e., with recognizing and
understanding sounds. Probably different portions of the cortex near
the auditory-sensory center have to do with different sorts of
auditory perception. At least, we sometimes find individuals who, as a
result of injury or disease affecting this general region, are unable
any longer to follow and appreciate music. They cannot "catch the
tune" any longer, though they may have been fine musicians before this
portion of their cortex was destroyed. In other cases, we find,
instead of this music deafness, the word deafness mentioned just
above.
The jargon talk that so often accompanies word deafness reminds us of
the fact that speech is first of all auditory to the child. He
understands what is said to him before he talks himself, and his
vocabulary for purposes of understanding always remains ahead of his
speaking vocabulary. It appears that this precedence of auditory
speech over motor remains the fact throughout life, in most persons,
and that the auditory speech center is the most fundamental of all the
speech centers, of which there is one more not yet mentioned, used in
reading.
{61}
[Illustration: Fig. 17.--(From Cajal.) Magnified sections through the
cortex, to show the complexity of its inner structure. One view shows
nerve cells and their dendrites, with only a few axons, while the
other shows axons, outgoing and incoming, and some of their fine
branches. Imagine one view superimposed upon the other, and you get
some idea of the intricate interweaving of axons and dendrites that
occurs in the cortex.]
{62}
The Visual Centers
There is a visual-sensory area in the occipital lobe, at the back of
the brain, that is connected with the eye in the same way as the
auditory center is connected with the ear. Without it, the individual
still shows the pupillary reflex to light, but has no sensations of
sight. He is blind.
[Illustration: Fig. 18.--Vertical cross-section through the brain,
showing the cortex on the outside, the thalamus and other interior
masses of gray matter, some of the paths to and from the cortex, and
the callosum or bridge of axons connecting the two cerebral
hemispheres. The "Motor path" is the pyramidal tract, only the
beginning of which is shown here, its further course being indicated
in Fig. 14. (Figure text: tactile path, motor path, auditory path,
callosum, thalamus, olfactory area)]
This visual-sensory area occupies only a small portion of the
occipital lobe, and yet practically the whole lobe is concerned with
vision. Some portions of the lobe are concerned in perceiving words in
reading, and without them the individual is "word blind". Other
portions are concerned in perceiving (recognizing, understanding) seen
objects, and without them the individual is "object blind". Other {63}
portions are concerned in perceiving color relations, and still other
portions in perceiving spatial relations through the sense of sight
and so knowing where seen objects are and being able to guide one's
movements by sight.
Cortical Centers for the Other Senses
There is an olfactory area in a rather secluded part of the cortex,
and this is related to the sense of smell in the same general way.
Probably there is a similar taste center, but it has not been
definitely located. Then there is a large and important area called
the "somesthetic", connected with the body senses generally, i.e.,
chiefly with the skin and muscle senses. This area is located in a
narrow strip just back of the central fissure, extending parallel to
the motor area which lies just in front of the fissure, and
corresponding part for part with it, so that the sensory area for the
legs lies just behind the motor area for the legs, and so on.
Destruction of any part of this somesthetic area brings loss of the
sensations from the corresponding part of the body.
Just behind this direct sensory center for the body, in the parietal
lobe, are portions of the cortex concerned in perceiving facts by aid
of the body senses. Perception of size and shape by the sense of
touch, perception of weight by the muscle sense, perception of degrees
of warmth and cold by the temperature sense, are dependent on the
parietal lobe and disappear when the cortex of this region is
destroyed. It appears that there is a sort of hierarchy of centers
here, as in the motor region and probably also in the visual and
auditory regions. Skill in handling objects is partly dependent on the
"feel" of the objects and so is impaired by injuries to the parietal
lobe, as well as by injury to the frontal lobe; and knowing how to
manage a fairly complex situation, as in lighting a fire when you have
the various {64} materials assembled before you, seems also to depend
largely on this part of the cortex.
Lower Sensory Centers
[Illustration: Fig. 19.--Sensory path from the skin of any portion of
the trunk or limbs. The path consists of three neurones, the cell body
of the first lying just outside the spinal cord, that of the second
lying in the cord, and that of the third lying in the thalamus. The
last part of this path is the "Tactile path," shown in Fig. 18.
(Figure text: cortex, thalamus, cord, skin)]
As already indicated, no portion of the cortex, not even the sensory
areas, is directly connected with any sense organ. The sensory axons
from the skin, for example, terminate in the spinal cord, in what may
be called the lowest sensory centers. Here are nerve cells whose axons
pass up through the cord and brain stem to the thalamus or interbrain,
where they terminate in a second sensory center. And cells here send
their axons up to the somesthetic area of the cortex.
{65}
The thalamus is remarkable as an intermediate center for all the
senses, except smell; but exactly what is accomplished by this big
intermediate sensory center remains rather a mystery, though it
certainly appears that the thalamus has something to do with feeling
and emotion.
The Cerebellum
Regarding the cerebellum, there is much knowledge at hand, but it is
difficult to give the gist of it in a few words. On the one hand, the
cerebellum receives a vast number of axons from the lower sensory
centers; while, on the other hand, it certainly has nothing to do with
conscious sensation or perception. Its use seems to be motor. It has
much to do with maintaining the equilibrium of the body, and probably
also with maintaining the steadiness and general efficiency of
muscular contraction. Though it has no known sensory or intellectual
functions, it is very closely connected with the cerebrum, receiving a
tremendous bundle of axons from different parts of the cerebrum, by
way of the brain stem. Possibly these are related to motor activity.
The phrenologists taught that the cerebellum was the center for the
sexual instinct, but there is no evidence in favor of this guess.
Different Levels of Reaction
Let a noise strike the ear and start nerve currents in along the
auditory nerve, passing through the lowest and intermediate centers
and reaching the auditory-sensory area of the cortex. When this last
is aroused to activity, we have a sensation of sound, which is the
first conscious reaction to the external stimulus. Axons running from
the auditory-sensory to the near-by cortex give a perception of some
fact indicated by the external stimulus, and this perception is a {66}
second and higher conscious reaction, which, to be sure, ordinarily
occurs so quickly after the first that introspection cannot
distinguish one as first and the other as second; but the facts of
brain injury, already mentioned, enable us to draw the distinction.
The perceived fact may call up a mental image, or a recognition of
some further fact less directly signified by the noise; these would be
reactions of still higher order. Much of the cortex is apparently not
very directly connected with either the sensory or the motor areas,
and probably is concerned somehow in the recognition of facts that are
only very indirectly indicated by any single sensory stimulus, or with
the planning of actions that only indirectly issue in muscular
movement.
On the sensory and intellectual side, the higher reactions follow the
lower: sensation arouses perception and perception thought. On the
motor side, the lower reactions are aroused by the higher. Thus the
speech center arouses the motor centers for the speech organs,
combining the action of these into the speaking of a word; and in a
similar way, it seems, the intention to speak a sentence expressing a
certain meaning acts as a stimulus to call up in order the separate
words that make the sentence. A general plan of action precedes and
arouses the particular acts and muscular movements that execute the
plan.
{67}
EXERCISES
1. Outline of the chapter. Fill in sub-topics under each of the
following heads:
A. Mental processes of all kinds are reactions.
B. The stimulus that directly arouses a mental process is often
"central".
C. Brain activities of all sorts influence the muscles by way
of the motor area and the lower motor centers.
D. Brain action in skilled movement.
E. Brain action in speech.
F. Brain action in sensation.
G. Brain action in recognizing seen or heard objects.
H. Relations of reactions of different levels.
2. Define and illustrate these classes of stimuli:
A. Peripheral:
(1) External.
(2) Internal.
B. Central.
3. Show by a diagram how one cortical center arouses another.
Compare the diagram in Fig. 9, p. 37.
4. Facilitation of the patellar reflex or "knee jerk". Let your
subject sit with one leg hanging freely from the knee down. With
the edge of your hand strike the patellar tendon just below the
knee cap. (a) Compare the reflex movement so obtained with a
voluntary imitation by the subject. Which is the quicker and
briefer? (b) Apply a fairly strong auditory stimulus (a sudden
noise) a fraction of a second before the tap on the tendon, and see
whether the reflex response is reinforced, (c) Ask the subject to
clench his fists or grit his teeth, and tap the tendon as he does
so. Reinforcement? (d) Where is the reflex center for the patellar
reflex, and whence comes the reinforcing influence?
5. Construct a diagram showing the different centers and connections
involved in making the skilled movement of writing; and consider
what loss of function would result from destruction of each of the
centers.
REFERENCES
Herrick's _Introduction to Neurology_, 1918, Chapter XX, on the
"Functions of the Cerebrum".
Stile's _Nervous System and Its Conservation_, Chapters X, XI
and XII.
{68}
CHAPTER IV
TENDENCIES TO REACTION
HOW MOTIVES INFLUENCE BEHAVIOR, AND HOW THEY FIT INTO A PSYCHOLOGY
WHICH SEEKS TO ANALYZE BEHAVIOR INTO REACTIONS.
One advantage of basing our psychology on _reactions_ is that it keeps
us "close to the ground", and prevents our discussions from sailing
off into the clouds of picturesque but fanciful interpretation.
Psychology is very apt to degenerate into a game of blowing bubbles,
unless we pin ourselves down to hard-headed ways of thinking. The
notion of a reaction is of great value here, just because it is so
hard-headed and concrete. Whenever we have any human action before us
for explanation, we have to ask what the stimulus is that arouses the
individual to activity, and how he responds. Stimulus-response
psychology is solid, and practical as well; for if it can establish
the laws of reaction, so as to predict what response will be made to a
given stimulus, and what stimulus can be depended on to arouse a
desired response, it furnishes the "knowledge that is power". Perhaps
no more suitable motto could be inscribed over the door of a
psychological laboratory than these two words, "Stimulus-Response."
Such a motto would not frighten away the modern introspectionists, for
they, no less than the behaviorists, could find a congenial home in a
stimulus-response laboratory. They would begin by studying sensations,
and, advancing to more complex responses, would observe the conscious
processes entering into the response.
{69}
But, however useful the reaction may be as affording a sound basis for
psychological study, we must not allow it to blind our eyes to any of
the real facts of mental life; and, at first thought, it seems as if
_motives, interests_ and _purposes_ did not fit into the
stimulus-response program. Many hard-headed psychologists have fought
shy of such matters, and some have flatly denied them any place in
scientific psychology. But let us see.
_S ---> R_
[Illustration: Fig. 20.--The symbol of stimulus-response psychology.
_S_ means the stimulus, and _R_ the response. The line between is the
connection from stimulus to response.]
Suppose we are looking out on a city street during the noon hour. We
see numbers of people who--lunch over, nothing to do till one
o'clock!--are standing or walking about, looking at anything that
chances to catch their eye, waving their hands to friends across the
street, whistling to a stray dog that comes past, or congregating
about an automobile that has broken down in the crowded thoroughfare.
These people are responding to stimuli, obviously enough, and there is
no difficulty in fitting their behavior into the stimulus-response
scheme.
But here comes some one who pays little attention to the sights and
sounds of the street, simply keeping his eyes open enough to avoid
colliding with any one else. He seems in a hurry, and we say of him,
"He must have business on hand; he has to keep an appointment or catch
a train". He is not simply responding to the stimuli that come to him,
but has some purpose of his own that directs his movements.
Here is another who, while not in such a hurry, is not idling by any
means, since he peers closely at the faces of the men, neglecting the
women, and seems to be looking for some one in particular; or,
perhaps, he neglects men and {70} women alike, and looks anxiously at
the ground, as if he had lost something. Some inner motive shuts him
off from most of the stimuli of the street, while making him extra
responsive to certain sorts of stimuli.
Purposive Behavior
Now it would be a great mistake to rule these purposeful individuals
out of our psychology. We wish to understand busy people as well as
idlers. What makes a man busy is some inner purpose or motive. He
still responds to present stimuli--otherwise he would be in a dream or
trance and out of all touch with what was going on about him--but his
actions are in part controlled by an inner motive.
To complete the foundations of our psychology, then, we need to fit
purpose into the general plan of stimulus and response. At first
thought, purpose seems a misfit here, since--
First, a purpose is an inner force, whereas what arouses a response
should be a stimulus, and typically an external stimulus. We do not
wish to drop back into the old "self-activity" psychology, which
thought of the individual as originating his acts from within himself.
But if we could show that a purpose is itself an inner response to
some external stimulus, and acts in its turn as a "central stimulus"
to further reactions, this difficulty would disappear.
Second, while a typical reaction, like the reflex or the simple
reaction of the experiment, is prompt and over with at once, a purpose
persists. It keeps the busy man, in our illustration, hurrying all the
way down the street and around the corner and how much farther we
cannot say. It is very different from a momentary response, or from a
stimulus that arouses a momentary response and nothing more.
Third, what persists, in purposive behavior, is the tendency {71}
towards some end or goal. The purposeful person wants something he has
not yet got, and is striving towards some future result. Whereas a
stimulus pushes him from behind, a goal beckons to him from ahead.
This element of action directed towards some end is absent from the
simple response to a stimulus.
In short, we have to find room in our stimulus-response psychology for
action persistently steered in a certain direction by some cause
acting from within the individual. We must find room for _internal_
states that _last_ for a time and _direct_ action. In addition, we
sometimes, though not always, need to find room for conscious
foreknowledge of the goal towards which the action is directed.
[Illustration: Fig. 21.--The stimulus-response scheme complicated to
allow for the existence of T, an inner motive or tendency, which,
aroused by an external stimulus, itself arouses a motor response. If
the reaction-tendency were linked so firmly to a single response as to
arouse that response with infallible certainty and promptness, then it
would be superfluous for psychology to speak of a tendency at all. But
often quite a series of responses, R1, R2, etc., follows upon a single
stimulus, all tending towards the same end-result, such as escape; and
then the notion of a "tendency" is by no means superfluous.]
"Purpose" is not the best general term to cover all the internal
factors that direct activity, since this word rather implies foresight
of the goal, which demands the intellectual ability to imagine a
result not present to the senses. This highest level of inner control
over one's behavior had best be left for consideration in later
chapters on imagination and will. There are two levels below this. In
the middle level, the individual has an inner steer towards a certain
result, though without conscious foresight of that result. At the
lowest level, we can scarcely speak of the individual as being
directed towards any precise goal, but still his {72} internal state
is such as to predispose him for certain reactions and against other
reactions.
The lowest level, that of organic states, is typified by fatigue. The
middle level, that of internal steer, is typified by the hunting dog,
striving towards his prey, though not, as far as we know, having any
clear idea of the result at which his actions are aimed. The highest
level, that of conscious purpose, is represented by any one who knows
exactly what he wants and means to get.
No single word in the language stands out clearly as the proper term
to cover all three levels. "Motives" would serve, if we agree at the
outset that a motive is not always clearly conscious or definite, but
may be any inner state or force that drives the individual in a given
direction. "Wants" or "needs" might be substituted for "motives", and
would apply better than "motives" to the lowest of our three levels.
"Tendencies", or "tendencies to reaction", carries about the right
meaning, namely that the individual, because of his internal state,
tends towards a certain action. "Determining tendencies" (perhaps
better, "directive tendencies") is a term that has been much used in
psychology, with the meaning that the inner tendency determines or
directs behavior. Much used also are "adjustment" and "mental set",
the idea here being to liken the individual to an adjustable machine
which can be set for one or another sort of work. Often "preparation"
or "readiness for action" is the best expression.
Organic States that Influence Behavior
Beginning at the lowest of our three levels, let us observe not even
the simplest animal, but a single muscle. If we give a muscle electric
shocks as stimuli, it responds to each shock by contracting. To a weak
stimulus, the response is weak; {73} to a strong stimulus, strong. But
now let us apply a long series of equal shocks of moderate intensity,
one shock every two seconds. Then we shall get from the muscle what is
called a "fatigue curve", the response growing weaker and weaker, in
spite of the continued equality of the stimuli. How is such a thing
possible? Evidently because the inner condition of the muscle has been
altered by its long-continued activity. The muscle has become
fatigued, and physiologists, examining into the nature of this
fatigue, have found the muscle to be poisoned by "fatigue substances"
produced by its own activity. Muscular contraction depends on the
oxidation of fuel, and produces oxidized wastes, of which carbon
dioxide is the best known; and these waste products, being produced in
continued strong activity faster than the blood can carry them away,
accumulate in the muscle and partially poison it. The "organic state"
is here definitely chemical.
[Illustration: Fig. 22.--Fatigue curve of a muscle. The vertical lines
record a series of successive contractions of the muscle, and the
height of each line indicates the force of the contraction. Read from
left to right.]
This simple experiment is worth thinking over. Each muscular
contraction is a response to an electric stimulus, but the force of
the contraction is determined in part by the internal state of the
muscle. Fatigue is an _inner_ state of the muscle that _persists_ for
a time (till the blood carries away the wastes), and that
_predisposes_ the muscle _towards_ a certain kind of response, namely,
weak response. Thus the three characteristics of purposive behavior
that seemed so {74} difficult to fit into the scheme of stimulus and
response are all here in a rudimentary form.
But notice this fact also: the inner condition of _muscular fatigue is
itself a response_ to external stimuli. It is part and parcel of the
total muscular response to a stimulus. The total response includes an
internal change of condition, which, persisting for a time, is a
factor in determining how the muscle shall respond to later stimuli.
These facts afford, in a simple form, the solution of our problem.
Before leaving the muscle, let us take note of one further fact. If
you examine the "fatigue curve" closely, you will see that a perfectly
fresh muscle _gains_ in strength from its first few responses. It is
said to "warm up" through exercise; and the inner nature of this
warming up has been found to consist in a moderate accumulation of the
same products which, in greater accumulation, produce fatigue. The
warmed-up condition is then another instance of an "organic state".
There will be more to say of "organic states" when we come to the
emotions. For the present, do not the facts already cited compel us to
enlarge somewhat the conception of a reaction as we left it in the
preceding chapters? Besides the external response, there is often an
internal response to a stimulus, a changed organic state that persists
for a time and has an influence on behavior. The motor response to a
given stimulus is determined partly by that stimulus, and partly by
the organic state left behind by just preceding stimuli. You cannot
predict what response will be made to a given stimulus, unless you
know the organic state present when the stimulus arrives.
Preparation for Action
At the second level, the inner state that partly governs the response
is more neural than chemical, and is directed {75} specifically
towards a certain end-result. As good an instance as any is afforded
by the "simple reaction", described in an earlier chapter. If the
subject in that experiment is to raise his finger promptly from the
telegraph key on hearing a given sound, he must be _prepared_, for there
is no permanent reflex connection between this particular stimulus and
this particular response. You tell your subject to be ready, whereupon
he places his finger on the key, and gets all ready for this
particular stimulus and response. The response is determined as much
by his inner state of readiness as by the stimulus. Indeed, he
sometimes gets too ready, and makes the response before he receives
the stimulus.
The preparation in such a case is more specific, less a general
organic state, than in the previous cases of fatigue, etc. It is
confined for the most part to the nervous system and the sense organ
and muscles that are to be used. In an untrained subject, it includes
a conscious purpose to make the finger movement quickly when the sound
is heard; but as he becomes used to the experiment he loses clear
consciousness of what he is to do. He is, as a matter of fact, ready
for a specific reaction, but all he is conscious of is a general
readiness. He feels ready for what is coming, but does not have to
keep his mind on it, since the specific neural adjustment has become
automatic with continued use.
Examples of internal states of preparedness might be multiplied
indefinitely, and it may be worth while to consider a few more, and
try out on them the formula that has already been suggested, to the
effect that preparation is an inner adjustment for a specific
reaction, set up in response to some stimulus (like the "Ready!"
signal), persisting for a time, and predisposing the individual to
make the specified reaction whenever a suitable stimulus for it
arrives. The preparation may or may not be conscious. It might be
named "orientation" or "steer", with the meaning that {76} the
individual is headed or directed towards a certain end-result. It is
like so setting the rudder of a sailboat that, when a puff of wind
arrives, the boat will respond by turning to the one side.
The runner on the mark, "set" for a quick start, is a perfect picture
of preparedness. Here the onlookers can see the preparation, since the
ready signal has aroused visible muscular response in the shape of a
crouching position. It is not simple crouching, but "crouching to
spring." But if the onlookers imagine themselves to be seeing the
whole preparation--if they suppose the preparation to be simply an
affair of the muscles--they overlook the established fact that the
muscles are held in action by the nerve centers, and would relax
instantly if the nerve centers should stop acting. The preparation is
neural more than muscular. The neural apparatus is set to respond to
the pistol shot by strong discharge into the leg muscles.
What the animal psychologists have called the _delayed reaction_ is a
very instructive example of preparation. An animal is placed before a
row of three food boxes, all looking just alike, two of them, however,
being locked while the third is unlocked. Sometimes one is unlocked
and sometimes another, and the one which at any time is unlocked is
designated by an electric bulb lighted above the door. The animal is
first trained to go to whichever box shows the light; he always gets
food from the lighted box. When he has thoroughly learned to respond
in this way, the "delayed reaction" experiment begins. Now the animal
is held while the light is burning, and only released a certain time
after the light is out, and the question is whether, after this delay,
he will still follow the signal and go straight to the right door. It
is found that he will do so, provided the delay is not too long--how
long depends on the animal. With rats the delay cannot exceed 5
seconds, with cats it can reach 18 {77} seconds, with dogs 1 to 3
minutes, with children (in a similar test) it increased from 20
seconds at the age of fifteen months to 50 seconds at two and a half
years, and to 20 minutes or more at the age of five years.
Rats and cats, in this experiment, need to keep their heads or bodies
turned towards the designated box during the interval between the
signal and the release; or else lose their orientation. Some dogs,
however, and children generally, can shift their position and still,
through some inner orientation, react correctly when released. The
point of the experiment is that the light signal puts the animal or
child into a state tending towards a certain result, and that, when
that result is not immediately attainable, the state persists for a
time and produces results a little later.
Preparatory Reactions
In the delayed reaction, the inner orientation does little during the
interval before the final reaction, except to maintain a readiness for
making that reaction; but often "preparatory reactions" occur before
the final reaction can take place. Suppose you whistle for your dog
when he is some distance off and out of sight. You give one loud
whistle and wait. Presently the dog swings around the corner and
dashes up to you. Now, what kept the dog running towards you after
your whistle had ceased and before he caught sight of you? Evidently
he was directed towards the end-result of reaching you, and this
directing tendency governed his movements during the process. He made
many preparatory reactions on the way to his final reaction of jumping
up on you; and these preparatory reactions were, of course, responses
to the particular trees he had to dodge, and the ditches he had to
jump; but they were at the same time governed by the inner state set
up in him by your {78 } whistle. This inner state favored certain
reactions and excluded others that would have occurred if the dog had
not been in a hurry. He passed another dog on the way without so much
as saying, "How d'ye do?" And he responded to a fence by leaping over
it, instead of trotting around through the gate. That is to say, the
inner state set up in him by your whistle _facilitated_ reactions that
were preparatory to the final reaction, and _inhibited_ reactions that
were not in that line.
A hunting dog following the trail furnishes another good example of a
directive tendency. Give a bloodhound the scent of a particular man
and he will follow that scent persistently, not turning aside to
respond to stimuli that would otherwise influence him, nor even to
follow the scent of another man. Evidently an inner neural adjustment
has been set up in him predisposing him to respond to a certain
stimulus and not to others.
The homing of the carrier pigeon is a good instance of activity
directed in part by an inner adjustment, since, when released at a
distance from home, he is evidently "set" to get back home, and often
persists and reaches home after a very long flight. Or, take the
parallel case of the terns, birds which nest on a little island not
far from Key West. Of ten birds taken from their nests and transported
on shipboard out into the middle of the Gulf of Mexico and released
500 miles from home, eight reappeared at their nests after intervals
varying from four to eight days. How they found their way over the
open sea remains a mystery, but one thing is clear: they persisted in
a certain line of activity until a certain end-result was reached, on
which this line of activity ceased.
One characteristic of tendencies that has not previously been
mentioned comes out in this example. When a tendency has been aroused,
the animal (or man) is tense and {79} restless till the goal has been
reached, and then quiets down. The animal may or may not be clearly
conscious of the goal, but he is restless till the goal has been
attained, and his restlessness then ceases. In terms of behavior, what
we see is a series of actions which continues till a certain result
has been reached and then gives way to rest. Introspectively, what we
feel (apart from any clear mental picture of the goal) is a
restlessness and tenseness during a series of acts, giving way to
relief and satisfaction when a certain result has been reached.
A hungry or thirsty animal is restless; he _seeks_ food or drink,
which means that he is making a series of preparatory reactions, which
continues till food or drink has been found, and terminates in the
end-reaction of eating or drinking.
What the Preparatory Reactions Accomplish
The behavior of a hungry or thirsty individual is worth some further
attention--for it is the business of psychology to interest itself in
the most commonplace happenings, to wonder about things that usually
pass for matters of course, and, if not to find "sermons in stones",
to derive high instruction from very lowly forms of animal behavior.
Now, what is hunger? Fundamentally an organic state; next, a sensation
produced by this organic state acting on the internal sensory nerves,
and through them arousing in the nerve centers an adjustment or
tendency towards a certain end-reaction, namely, eating. Now, I ask
you, if hunger is a stimulus to the eating movements, why does not the
hungry individual eat at once? Why, at least, does he not go through
the motions of eating? You say, because he has nothing to eat. But he
could still make the movements; there is no physical impossibility in
his making chewing and swallowing movements without the presence of
food. {80} Speaking rationally, you perhaps say that he does not make
these movements because he sees they would be of no use without food
to chew; but this explanation would scarcely apply to the lower sorts
of animal, and besides, you do not have to check your jaws by any such
rational considerations. They simply do not start to chew except when
food is in the mouth. Well, then, you say, chewing is a response to
the presence of food in the mouth; and taking food into the mouth is a
response to the stimulus of actually present food. The response does
not occur unless the stimulus is present; that is simple.
Not quite so simple, either. Unless one is hungry, the presence of
food does not arouse the feeding reaction; and even food actually
present in the mouth will be spewed out instead of chewed and
swallowed, if one is already satiated. Try to get a baby to take more
from his bottle than he wants! Eating only occurs when one is _both_
hungry and in the presence of food. Two conditions must be met: the
internal state of hunger and the external stimulus of food; then, and
then only, will the eating reaction take place.
Hunger, though a tendency to eat, does not arouse the eating movements
while the stimulus of present food is lacking; but, for all that,
hunger does arouse immediate action. It typically arouses the
preparatory reactions of seeking food. Any such reaction is at the
same time a response to some actually present stimulus. Just as the
dog coming at your whistle was responding every instant of his
progress to some particular object--leaping fences, dodging trees--so
the dog aroused to action by the pangs of hunger begins at once to
respond to present objects. He does not start to eat them, because
they are not the sort of stimuli that produce this response, but he
responds by dodging them or finding his way by them in his quest for
food. The responses that the hungry dog makes to other objects than
{81} food are preparatory reactions, and these, if successful, put the
dog in the presence of food. That is to say, the _preparatory
reactions provide the stimulus that is necessary to arouse the
end-reaction_. They bring the individual to the stimulus, or the
stimulus to the individual.
[Illustration: Fig. 23.--A stimulus arouses the tendency towards the
end-reaction, R, but (as indicated by the dotted line), T is not by
itself sufficient to arouse R; but T can and does arouse P, a
preparatory reaction, and P (or some external result directly produced
by P), coöperating with T, gives rise to R.]
What we can say about the modus operandi of hunger, then, amounts to
this: Hunger is an inner state and adjustment predisposing the
individual to make eating movements in response to the stimulus of
present food; in the absence of food, hunger predisposes to such other
responses to various stimuli as will bring the food stimulus into
play, and thus complete the conditions necessary for the eating
reaction. In general, _an aroused reaction-tendency predisposes the
individual to make a certain end-reaction when the proper stimulus for
that reaction is present; otherwise, it predisposes him to respond to
other stimuli, which are present, by preparatory reactions that
eventually bring to bear on the individual the stimulus required to
arouse the end-reaction_.
Let us apply our formula to one more simple case. While reading in the
late afternoon, I find the daylight growing dim, rise and turn on the
electric light. The stimulus that sets this series of acts going is
the dim light; the first, inner response is a _need_ for light. This
need tends, by force of habit, to make me turn the button, but it does
not make me execute this movement in the air. I only make this
movement when the button is in reaching distance. My first {82}
reaction, rising from my chair, is preparatory and brings the button
close enough to act as a stimulus for the hand reaction. The button
within reach is not by itself sufficient to arouse the turning
reaction, nor is the need for light alone sufficient. The two
conditions must be present together, and the preparatory reaction is
such that, given the need, the other condition will be met and the
reaction then aroused.
What a Tendency Is, in Terms of Nerve Action
Very little need be added to our neural conception of a reaction in
order to get a satisfactory conception of a tendency to reaction.
Principally, we must add this fact, that a nerve center aroused to
activity does not always discharge instantly and completely into the
muscles, or into some other center, and come to rest itself. It does
so, usually, in the case of a reflex, and in other momentary
reactions; as when A makes you think of B, and B at once of C, and so
on, each thought occupying you but a moment. But a tendency means the
arousing of a nerve center under conditions which do not allow that
center to discharge at once. The center remains in a condition of
tension; energy is dammed up there, unable to find an outlet.
We have already seen what the conditions are that cause this damming
up of energy. The center that is aroused tends to arouse in turn some
lower motor center, but by itself does not have complete control over
that lower center, since the lower center also requires a certain
external stimulus in order to arouse it to the discharging point.
Until the proper external stimulus arrives to complete the arousal of
the lower center, the higher center cannot discharge its energy.
When there is an "organic state" present, such as hunger or thirst,
this may act as a persistent stimulus to the sensory nerves and
through them to the higher center in {83} question; and then we can
readily understand how it is that the center remains active until the
organic state is relieved. But where there is no such persistent
organic stimulus, as there can scarcely be in the case of the
bloodhound or of the man hurrying to a train or seeking in the crowd
for a friend, there we have to suppose that a center, once aroused to
activity and prevented from complete discharge, remains active by
virtue of energy dammed up in itself. There is pretty good
physiological evidence that this sort of thing is a fundamental fact;
for there are certain rhythmical reflexes, like scratching or
stepping, that, when started going by a momentary sensory stimulus,
keep it up for a time after the stimulus has ceased. There seems to be
no doubt that a nerve center, once aroused, may stay aroused for a
time.
The "dammed-up energy" here is not to be confused with the "stored
energy" spoken of under the head of reactions. We said, in that
connection, that a stimulus released energy stored in the organism.
That, however, was _potential_ energy, dormant within the organism
till aroused; but what we have here in mind is active or _kinetic_
energy. Stored energy is like that of coal in the bin; dammed-up
energy is like that of steam in the boiler.
Dammed-up energy in the nerve centers accounts for the persistence of
a tendency to reaction after the stimulus has ceased. It accounts for
the "delayed reaction" and similar cases. But how shall we account for
preparatory reactions? We have a nerve center in an active state,
tending to discharge into a certain lower motor center, but unable to
do so because a peripheral stimulus is necessary, in addition, in
order to arouse this lower center. Then we find the higher center
discharging into _other_ lower centers, and so giving rise to
preparatory reactions. More precisely, what we find is that the higher
center facilitates the response {84} of certain lower centers to their
proper peripheral stimuli, while inhibiting the response of other
lower centers to their appropriate stimuli. This is the same sort of
thing that we observe in all control exerted by a higher center over a
lower. It means that the higher center, besides its main line of
connection with the lower center that will give the end-reaction, has
minor lines of connection with certain other lower centers; some of
these centers it facilitates and others it inhibits. These connections
between the main and the subordinate centers may have been established
by inborn nature, or by previous training, as will be explained in
later chapters.
The action of the main center on the subordinate centers concerned in
executing preparatory reactions does not relieve the tension in the
main center. The dammed-up energy stays there till the proper stimulus
is procured for arousing the end-reaction, and then escapes through
its main channel of discharge, and the main center then finally comes
to rest.
It may fairly be urged that no violence has been done to the general
conception of a reaction by these additions, and also that with the
additions the notion of a reaction has room for tendencies or inner
adjustments. So that we conclude that stimulus-response psychology is
adequate to the job, and will do justice to all forms of human
behavior. It has a place for sensations, perceptions and thoughts, as
we saw in the preceding chapter, and it has a place also for purposes,
desires and motives generally.
Motives
In the present chapter, desirous of "keeping close to the ground", we
have said little of distinctively human motives. That will come later.
In general, a motive is a tendency towards a certain end-result or
end-reaction, a tendency which is itself aroused by some stimulus, and
which {85} persists for a time because its end-reaction is not at once
made. The end-reaction is not made at once because it can only be
aroused by an appropriate stimulus, acting in conjunction with the
motive. But the motive, persisting in its inner activity, facilitates
reactions to certain stimuli and inhibits others. The reactions it
facilitates are preparatory to the end-reaction, in that they provide
the necessary conditions for that reaction to occur, which means that
they bring to bear on the individual the necessary stimulus which can
arouse the end-reaction. The restlessness that characterizes an
individual driven by an inner motive gives way to rest and
satisfaction when the end-result is reached.
Motives range from the primitive or primal, like hunger, to the very
advanced, such as zeal for a cause. They range from the momentary,
illustrated by the need for more light in reading, to the great
permanent forces of life, like _amour propre_ and _esprit de corps_.
But the permanent motives are not always active; they sleep and are
awakened again by appropriate stimuli.
In everyday speech we are apt to use the words "motive" and "reason"
interchangeably, as in asking some one what his "motive", or what his
"reason" is for doing so and so. A motive, however, is not necessarily
a reason, nor a reason a motive. A reason is thought-out and
conscious, which a motive need not be. On the other hand, a reason
does not become a motive unless it takes hold of us and arouses a
genuine tendency towards the planned result. You may prove to me,
logically, the desirability of a course of action, but your reasons do
not necessarily make me desire it. You can give a child excellent
reasons for studying his lessons, but you have to stir some real
motive of child life in order to get action. In the highest type of
conduct, to be sure, motive and reason pull together, reason showing
the way to the goal at which motive is aimed.
{86}
EXERCISES
1. Complete the following outline of the chapter, by filling in
main headings to fit the subordinate headings that are given below:
A. _________
(1) It keeps close to the facts.
(2) It has room for introspective as well as behavior study.
(3) It can be applied practically.
B. _________
(1) A stimulus is typically external, a purpose internal.
(2) A stimulus typically acts for a moment, a purpose persists
for some time.
(3) A stimulus is not directed towards a result, a purpose is
so directed.
C. _________
(1) Organic or physiological states that predispose towards
certain forms of behavior.
(2) Inner adjustments towards certain results, without
foresight of the results.
(3) Conscious purpose.
D. _________
(1) They are aroused by stimuli.
(2) They persist for a time.
(3) They influence the response to other stimuli.
E. _________
(1) They are neural rather than chemical.
(2) They amount to a preparation or readiness for a certain
response.
(3) They persist sometimes for only a few seconds, sometimes
for many minutes at least.
F. _________
(1) A whole series of acts may be set going by a single stimulus.
(2) The series comes to an end when a certain result has been
reached.
(3) Each act in the series is a response to some particular
stimulus, and yet would not be aroused by that stimulus
except for the active adjustment towards the end-result.
{87}
(4) The end-result cannot be reached until a particular
stimulus helps the adjustment to arouse the end-reaction.
(5) The preliminary acts in the series bring the required
stimulus that can give the end-reaction.
G. _______
(1) It may be kept active by a continuing peripheral stimulus.
(2) It may be unable to discharge fully because its main path of
discharge is blocked.
H. _______
(1) The main center has minor connections with other
centers, in addition to its main path of discharge.
(2) The persisting activity of the main center influences
other centers by way of facilitation and inhibition.
2. Fill in the blanks in the following paragraph:
"A motive or (1) is a reaction that has not yet come off. It has
been (2) by some stimulus, and it tends towards a certain (3),
which however it is unable of itself to produce, but requires the
assistance of another (4) which is not yet present. The motive
gives rise to (5) responses, which, if (6), finally bring the
required (7), and this, combined with the (8) arouses the (9), and
so brings the whole (10) of acts to a close."
3. Cite cases illustrating the importance of preparatory adjustment
(a) for securing prompt reaction, and
(b) for securing keen observation.
4. Cite a case where some need or desire gives rise to a series of
preparatory reactions.
5. Cite a case where a need or desire leads to the omission
(inhibition) of acts that would otherwise have occurred.
6. What is meant by the last sentence in the chapter?
7. An experiment on the "delayed reaction". Take two sheets of
paper, and on each write the letters A, B, C, D, E, and F,
scattering them irregularly over the sheet. The task, in general,
is now to take aim at one of the letters, while your hand, holding
a pencil, is raised to the side of your head, and then to close the
eyes and strike at the letter aimed for. First aim at A, and mark
the point hit with an a, then the same with B, and so on. With the
first sheet, strike as soon as you have got your aim and closed
your eyes; but with the second sheet, aim, close your eyes, and
count ten slowly before striking, keeping the eyes closed till the
stroke has been made. Two sorts of observation should now be made:
first, introspective--record at once what you can of the way you
kept your aim during the delay. Second, objective--measure the
errors, and determine how much the delay affected your aim. What
conclusions can you draw from the experiment?
{88}
REFERENCES
On the "delayed reaction", see Walter S. Hunter, "The Delayed Reaction
in Animals and Children", _Behavior Monographs_, No. 6, 1913. A brief
summary of this work can also be found in Hunter's _General
Psychology_, 1919, pp. 31-33.
On the homing of pigeons and terns, see Watson and Lashley, _An
Historical and Experimental Study of Homing_, published by the
Carnegie Institution of Washington, 1915.
Interesting examples of changed organic states affecting the behavior
of unicellular animals are given by Jennings in his _Behavior of the
Lower Organisms_, 1906, and by Margaret F. Washburn in _The Animal
Mind_, 2nd edition, 1917, pp. 246-257.
{89}
CHAPTER V
NATIVE AND ACQUIRED TRAITS
SOME RESPONSES ARE PROVIDED BY NATURE, WHILE
OTHERS HAVE TO BE LEARNED BY EXPERIENCE
John Doe is a strongly built man, over six feet high, with big bones
and muscles, erect, vigorous, with plenty of color in his face,
dark-haired, blue-eyed, clean-shaven, with a scar on his cheek, broad
face and large ears. He is easy-going, even-tempered, fond of children
and also of women, rather slangy and even profane in his talk, has a
deep, sonorous voice and can carry the bass in a chorus. He is handy
with tools, can drive or repair an automobile, is a fairly good carpet
salesman, but much prefers out-of-door work. Rather free in spending
his money, he has never run into debt except on one occasion, which
turned out badly for him. Which of these traits of John Doe are native
and which are acquired? How far are his physical, mental and moral
characteristics the result of his "original nature" and how far have
they been ingrained in him or imposed upon him by his training and
environment?
The distinction between native and acquired is clearest in the field
of anatomy. Hair color and eye color are evidently native, and so, in
the main, is the size of the body, though undoubtedly growth may be
stunted by poor nutrition, and the individual fail to reach his
"natural" height and weight. On the other hand, scars, tan, and the
after-effects of disease or injury, are evidently acquired. Of
movements, the native character of the reflexes has already been
noted, and it is clear that skill in handling tools or {90} managing
the voice is learned, though the individual may have a natural
aptitude for these performances. Temperament and emotional traits we
usually think of as belonging to a man's "nature", though we have to
admit that a naturally cheerful disposition may be soured by ill
treatment. On the other hand, while we reckon habits, such as
profanity, or free spending, or an erect carriage, as belonging with
the acquired traits, we know that some natures are prone to certain
habits, and other natures to other habits. Thus the effects of
"nature" and "experience" are almost inextricably interwoven in the
behavior of an adult person.
Difficult as it certainly is to separate the native from the acquired
in human action, the attempt must be made. We cannot dodge so
fundamental a problem. Scientifically it is important as the
starting-point of a genetic study; we must know where the individual
starts in order to understand the course of his development.
Practically it is important because there is reason to believe that
native traits are deeply seated and not easily eradicated, even though
they can be modified and specialized in different ways. If a habit is
not simply a habit, but at the same time a means of gratifying some
natural tendency, then it is almost imperative to find a substitute
gratification in order to eliminate the habit. The individual's nature
also sets limits beyond which he cannot be brought by no matter how
much training and effort; and this is true of mental development as
well as of physical.
The Source of Native Traits
"Native" means a little more than "congenital." A child may be born
blind, having been infected by disease germs shortly before birth; he
may be congenitally an idiot because of head injury during a difficult
birth; or his mentality may have been impaired, during his uterine
life, by {91} alcohol reaching his brain from a drunken mother. Such
traits are congenital, but acquired. Native traits date back to the
original constitution of the child, which was fully determined at the
time when his individual life began, nine months before birth. The
"fertilized ovum", formed by the combination of two cells, one from
each of the parents, though microscopic in size and a simple sphere in
shape, somehow contains the determiners for all the native or
inherited traits of the new individual.
It is very mysterious, certainly. This microscopic, featureless
creature is already a human individual, with certain of its future
traits--those that we call "native"--already settled. It is a human
being as distinguished from any other species, it is a white or
colored individual, male or female, blonde or brunette, short or tall,
stocky or slender, mentally gifted or deficient, perhaps a "born"
musician or adventurer or leader of men. These and all other native
traits are already determined and latent within it; and the only
question, regarding such traits, is whether the environment is going
to be such as to enable this young individual to live and mature and
unfold what is latent within it.
Reactions Appearing at Birth Must Be Native
For the first few months of the individual's existence, sheltered as
it is within the mother's body, there is no chance for any
acquisition, except of certain abnormalities such as were alluded to
above. What occurs during this prenatal period is natural development,
not learning or any effect of experience. The traits displayed by the
new-born child are, accordingly, native traits. His breathing, crying,
starting at a noise, squirming, stretching, grasping, sucking and
swallowing, and other movements made from birth on, are to be counted
as native reactions, that is to say, as {92} reactions executed by
sensory, muscular and nervous machinery that have become ready for use
by the mere process of natural growth. This is the first and clearest
sign of a native trait, that it shall appear at birth.
Reactions That Cannot Be Learned Must Be Native
But native traits continue to make their appearance as the child's
development proceeds after birth. Inherited anatomical traits, like
stature and build, hair color, beard, and shape of nose, though
certainly determined by native constitution, do not fully make their
appearance till maturity. In fact, what does maturity mean, except
that the natural characteristics have finally reached their complete
development? And it is as true of internal structure as of external,
that natural development, far from being complete at birth, keeps on
till maturity. The neurones continue to grow, and their synapses in
the nerve centers to become closer knit, just by virtue of natural
growth; and thus reflex arcs, and other reaction machinery, one by one
reach the ready-to-use stage during the individual's growing-up,
especially during the first few years. With the growth to a functional
condition of their sensori-neuro-muscular mechanisms, mental and motor
reactions that are native, though not present at birth, make their
appearance. The native intelligence of the child gradually unfolds,
likewise his special native "gifts" and his inherited emotional and
impulsive traits.
Of course it is more difficult to make sure that a trait is native
when it does not appear till some time after birth, for the chance of
acquiring it by a process of learning has to be taken into account. If
you can so control the conditions under which the young individual
grows as to eliminate the possibility of learning a certain act, then
you can {93} make sure whether the act is acquired or provided by the
native constitution.
Experimental Detection of Native Reactions
Take the question whether birds learn to fly or simply come to fly
when their natural development has gone far enough. The newly hatched
bird cannot fly; its muscles are not strong enough, its wings are not
feathered, and its nerve mechanism for coördinating the wing movements
has still some growth to make before being ready for use. But, under
ordinary conditions, the young bird has some chance to _learn_ flying,
by watching the old birds fly and by trying and gradually getting the
motion. The old birds, after a time, push the young ones from the nest
and seem, to our eyes, to be teaching them to fly. Experiment enables
us to decide the question. One of the earliest experiments in animal
psychology was made by Spalding in 1873. He took newly hatched birds
from the nest and shut each one separately in a little box that gave
it no chance to stretch its wings or to see other birds fly. Here he
fed and cared for them till the age at which flying usually begins,
and then released them. Off they flew, skilfully managing wings and
tail, swooping around the trees and soon disappearing from sight. A
very successful experiment!--and conclusive. The little birds had had
no chance to learn to fly, yet they flew. Flying must have come to
them in the natural course of growth.
Compare with this experiment another one no less successful, though it
turned out differently. To discover whether the song of the oriole is
fixed by nature or learned by imitation, Scott took some little ones,
just hatched, and brought them up away from older birds. After a time,
when growth had advanced to a certain stage, the birds began {94} to
sing. The elementary notes and rattles characteristic of the oriole
made their appearance, but were combined in unusual ways, so that the
characteristic song of the oriole did not appear, but a new song. When
these birds had grown up in the laboratory, other new-hatched orioles
were brought up with them, and adopted this new song; so that the
laboratory became the center for a new school of oriole music. The
experiment showed that the elements of the oriole's song were provided
by nature, while the combination of these elements was acquired by
imitation.
Probably this last is about the result one would get in the analogous
case of human speech, if a similar experiment should be tried on
children. Without an experiment, we have certain facts that point to a
conclusion. The child uses his vocal organs from birth on; and before
he reaches the age when he imitates the speech of others, he produces
various vowels and consonants, and even puts them together into simple
compounds, as "da-da" and "goo-goo." So far, deaf children do about
the same as others, affording additional evidence that so much of
speech is native. To get real speech, however, further combinations of
the speech movements must be made, and the combinations (words) must
have meaning attached to them. These higher achievements are evidently
the result of learning, since the child uses the words that it hears
spoken, and attaches the same meanings to them as people do about it.
The child comes to speak the language of those about it, without
regard to the speech of its ancestors. His "native language" is
therefore acquired, though the elements of vocal utterance are truly
native, and apparently are alike all over the world without regard to
the various languages spoken.
{95}
Is Walking Native or Acquired?
As another example of this same general problem of distinguishing
native from acquired reactions, and of the kind of evidence that
throws light on the problem in the absence of direct experiment, let
us consider the child's walking. Does the child learn to walk, or does
it simply _come_ to walk when its natural development has gone far
enough? We think the child learns to walk because it begins very
imperfectly and usually takes several weeks before it can be described
as really walking of itself. We even think we teach it to walk, though
when we examine our teaching we soon convince ourselves that we do not
know _how_ we walk, and that what we are doing with the baby is to
stimulate and encourage him to walk, protect him from hurting himself,
etc., rather than teaching him as we later teach the child to write.
An experiment to settle the matter might be conducted along the lines
of Spalding's experiment on the young birds. We might prevent the baby
from making any attempt to walk till it had fully reached the normal
age for walking, and then turn it loose and see whether it walked of
itself.
Such an experiment has never been made under strict laboratory
conditions; but here is a well-attested case that approximates to an
experiment. A little girl of seven months, a very active child, seemed
to want to get on her feet; but the doctor decided that her feet were
too small to use, and directed that she be put back in long dresses.
For four months she was kept in long dresses, and great care was
exercised never to place her on the floor without them. Then, one day,
she was set down without her dress, and immediately up she got and
walked; and from that moment she was very agile on her feet.
Another rather different case, but tending towards the {96} same
conclusion, is that of a little girl who, in contrast to the
preceding, gave her parents some anxiety because, up to the age of
seventeen months, she wouldn't walk. She would stand holding on, but
not trust herself to her feet alone. One noon her father came in from
his work and, removing his cuffs, laid them on the table. The little
girl crept to the table, and raised herself to a standing position,
holding on to the table. She then took a cuff in one hand, and
inserted the other hand into it, thus, for the first time, standing
unsupported. She put on the other cuff in like manner, and then
marched across the room, as proud as you please. For a few days she
could walk only with cuffs, but after that was able to dispense with
them. There are a few other cases, differing in details, but agreeing
on the main point, that the baby walked well on its first trial and
went through nothing that could properly be interpreted as a process
of learning.
It would really be very surprising if the human infant were left to
learn locomotion for himself, while all other animals have this power
by nature. Just because the human infant matures slowly, and learns a
vast deal while maturing, is no reason for overlooking the fact that
it does mature, i.e., that its native powers are gradually growing and
reaching the condition of being ready for use. The most probable
conception of "learning to walk," in the light of the evidence, is
about as follows. At the age when the child's bones and muscles have
become strong enough for walking, the nerve connections for
coördinating this complex movement have also just about reached the
stage of development when they are ready for business. The numerous
synapses in the nerve centers that must be traversed by nerve currents
in order to arouse the muscles to this particular act are not, we may
suppose, all ready at the same instant, and it takes some little time
for them to pass from {97} the stage when they will first conduct to
the stage when, having grown more, they conduct perfectly. In other
words, the neural mechanism for walking can function imperfectly
before it can function perfectly. It takes several weeks of growth to
pass from the barely functional condition to the fully functional
condition; and it is during these weeks that the child seems to be
learning to walk, while really his exercise of the partially developed
neural mechanisms has no effect except to hasten their growth to some
extent.
Universality as a Criterion of Native Reactions
The fundamental sign or criterion of a native trait, in accordance
with what we have been saying, is that it shall make its appearance
when there has been no chance to acquire it through experience. This
is the one perfect criterion; but unfortunately it cannot always be
applied, especially with a slowly maturing and much-learning species
such as the human. We need other criteria, and one of some value is
the criterion of _universality_.
Consider, for example, the attraction between the sexes, and ask
whether this represents a native tendency, or whether each individual
acquires it, as he does his "native language", by learning from his
elders. Before the body reaches sexual maturity, there has been
abundant opportunity for the quick-learning child to observe sex
attraction in older people. Yet it is highly improbable that the
liking for the other sex which he begins to show strongly in youth is
simply an acquired taste. It is improbable because the attraction
between the sexes is so universal not only among mankind but among
birds and mammals and, indeed, practically throughout the animal
kingdom.
Fighting is a similar case. Not so universal as the sex instinct, it
still appears almost universally among birds and mammals.
{98}
The human individual is an animal, and some of his native traits are
universal among animals. He is a vertebrate, and some of his traits,
though not present in all animals, are universal among vertebrates. He
is a mammal, with mammalian traits; a primate, with primate traits; a
man with human traits; a Chinaman or Indian or European with racial
traits; belongs to a more or less definite stock or breed within the
race, and possesses the traits that are common to members of that
stock; and the same with family traits. The criterion of universality,
in the light of these facts, comes down to this: that _when all
individuals having the same descent show a trait in common, that
trait is to be regarded as belonging to their native
constitution--unless evidence can be brought forward to the contrary_.
Smoking is universal among many Malay peoples, but we know, as a
historical fact, that it was introduced among them after the discovery
of America, not very many generations ago. Superstition is universal
among some peoples, but we see the superstitious beliefs and practices
taught by the older to the younger generation. Similarly with any
specific language. It may very well be true in such cases that the
universal practice appeals to some native tendency of the people; but
the specific practice is handed down by tradition and not by
inheritance.
Some Native Traits Are Far from Being Universal
Though the universality of a trait creates a certain presumption in
favor of its being native, the opposite is not always true, for a
trait may be native and yet appear in only a fraction of those who
have a common descent. Eye color is certainly native, and yet one of
two brothers may have blue eyes and the other brown. Mental deficiency
runs in families, but usually some members of such families have {99}
normal mentality. Genius is almost certainly a native trait, but it is
the reverse of universal. The fact is that, along with certain traits
that appear in all, the native constitution of a stock provides also
for traits that appear only sporadically. Enough has been said to show
that the criterion of universality is one that needs to be applied
with judgment.
Why Acquired Traits Differ from One Individual to Another
Acquired traits are on the whole much less universal, much more
individual, than native traits. They are readjustments of the
individual to environmental conditions; and, as the environment
varies, so the adjustments vary, even when native traits are the same.
Acquired traits are often specializations of the native traits, as any
specific language is a specialization of the vocal utterances that are
native and common to all men, and as the peculiar gait of an
individual is a specialization of the universal walking movement. The
gait differs with the environmental differences to which the
individual has adapted himself, and will be different in one who has
been accustomed to walk over rough ground and in one whose walking has
been done on the city streets.
_Acquired traits are not independent of native, but are developed on
the basis of the native traits_. They are acquired not by laying aside
native tendencies and working out something entirely new, but by
acting in accordance with the native tendencies and making such
readjustments as the environment demands. The acquisition of mental
traits is accomplished by the process of _learning_, and we shall
later have abundant occasion to examine it in more detail.
{100}
What Mental Traits Are Native?
For the present, let us simply take a brief survey of the mental
field, and notice what types of reactions are native and what
acquired. On the motor side, the reflexes are native, while habitual
and skilled movements are acquired. On the sensory side, nature
provides the use of the sense organs and the sensations immediately
resulting from their stimulation. The baby responds to touch, warmth,
cold, sound and light as soon as it is born, or practically so, and
undoubtedly has the corresponding sensations. In other words, the
rudiments of seeing, hearing, etc., are provided by nature. But when
we say, "I see a dog" we mean more than that we are getting certain
visual sensations; we mean that we see a known object or known sort of
object. This implies recognition of the object, either as an
individual thing or as one of a class; and this the baby can scarcely
be supposed to do at first. He sees the dog to the extent that he
responds by visual sensations to the light coming from the dog, but
not to the extent that he recognizes the dog as a dog. In short, the
_meanings_ of sensations are acquired, though the sensations
themselves are native.
Things come to be known by use of the senses, and when thus known are
not only recognized when present, but also remembered and thought of
when they are not present to the senses. Such memories and items of
knowledge, dependent as they are on experience, are to be reckoned
among the acquired reactions. Ideas or conceptions of things also
belong here.
Of the emotions, some are called "primary" or native--anger and fear
are examples--while others result from the compounding of these
primary emotions and are therefore acquired. As people and things come
to be known, emotional reactions become attached to them, and give
what {101} are often named "sentiments", such as love for this person,
contempt for that one, family pride, patriotism. These sentiments,
bound up as they are with knowledge and ideas, are certainly acquired.
Closely akin to the primary emotions are the native impulses, as the
impulse to eat, to cry, to laugh, to escape from danger, to resist
external compulsion and to overcome obstacles. The native impulses are
the raw material out of which the numerous acquired desires of child
and adult are formed. One sort of native impulse is the impulse to
notice or pay attention to certain sorts of stimuli. These native
interests of the child give birth to the various specialized interests
of the adult. The baby's attention to a bright light represents a
native interest; the older child's fixing his eyes on a dark brown
piece of chocolate represents an acquired interest which has developed
in a way that is easy to understand.
Finally, we must count among the native traits of the individual his
inherited aptitudes for certain kinds of work. One child shows a
natural aptitude for music, another for acting, another for
mathematics, another for mechanical things, another for language, and
so on. As any of these "natural gifts" is present in some degree in
nearly all members of the human family, and not to anything like the
same degree in animals, they are the characteristically human traits.
It is on the basis of such native aptitudes that each individual
proceeds, through the processes of learning, to build up his various
acquired abilities, such as the ability to sing, to speak a certain
language, to add, to work with tools, to perform athletic feats, and
to take part in social activities of various sorts.
Our next task will be to examine more closely the native equipment of
man, and after that to take up the process of learning, which is the
way reactions are acquired. First the native, then the acquired. The
acquired is based upon {102} the native. Acquired reactions are indeed
so numerous that we cannot attempt even to list them all, let alone
examine each one separately; but we can at least study the _way_ in
which they are acquired. Native reactions are much less numerous, so
that the student may hope to obtain a fairly comprehensive survey of
this field, though, of course, without much detail.
The general plan of this book, then, is as follows. Up to this point,
it has been providing a stock of methods and general conceptions to
serve as tools in psychological study: consciousness and behavior, the
introspective and objective methods, reactions and tendencies to
reaction, native and acquired, and the part played by the nervous
system. Next comes a survey of reactions provided by the native
constitution, and after that a study of the process of learning or
acquiring reactions. Finally, there are several chapters devoted to
such topics as imagination, reasoning and will, which are ways in
which the individual utilizes his whole equipment, native and
acquired, in meeting the exigencies of life.
{103}
EXERCISES
1. Outline the chapter.
2. When does the individual come into existence as an individual?
When does he begin to acquire traits? How long does he continue to
unfold his native traits, and how long does he continue to acquire
traits?
3. Which of the following elements of spoken language are native,
and which acquired?
(a) Production of voice by the vocal cords and air blast from the lungs.
(b) Varying the voice in loudness.
(c) Varying the voice in pitch.
(d) Production of vowels by different positions of the mouth.
(e) Production of consonants by lip and tongue movements.
(f) Combination of vowels and consonants into words.
(g) Combination of words into idioms and grammatical sentences,
(h) Attachment of meanings to words.
(i) Sweet-toned voice.
(j) Nasal twang.
(k) Fluency in speaking.
4. In each of the following reactions, decide whether the connection
of stimulus and response is probably native or acquired:
Stimulus Response
(a) a sudden noise starting
(b) a bright light blinking
(c) a bright light shading your eyes
(d) cold putting on coat
(e) cold shivering
(f) sight of a ball reaching for it
(g) ball in the hand throwing it
(h) slipping righting yourself
(i) row of objects counting them
(j) insulting language anger
REFERENCES
Edward L. Thorndike, in Chapter I of his _Educational Psychology,
Briefer Course_, 1914, gives a general survey of the native factors in
mental life and behavior.
{104}
Hollingworth and Poffenberger, in their _Applied Psychology_, 1917,
devote Chapters II and III to the matter of mental heredity.
Norsworthy and Whitley, in their _Psychology of Childhood_, devote
Chapters I and II to "original nature".
C. B. Davenport, in his _Heredity and Eugenics_, presents evidence of
the importance of heredity in determining mental and moral traits.
Yerkes and Bloomfleld, in a short article in the _Psychological
Bulletin_ for 1910, Vol. 7, pp. 253-263, under the title, "_Do Kittens
Instinctively Kill Mice?_", furnish a good illustration of the method
employed in distinguishing native from acquired reactions.
{105}
CHAPTER VI
INSTINCT
CONDUCT AS DETERMINED BY NATIVE REACTION-TENDENCIES
Instinct is native behavior. It is contrasted with habit, knowledge,
or anything in the way of learned reactions. When the mother wasp
gathers a store of food suitable for young wasps, lays eggs beside the
food and covers the whole with a wall of mud, we know that her
behavior is instinctive because she has had no possible chance to
learn from older wasps. She has never seen a wasp's nest made, for
when the last preceding crop of nests was being made she was herself
an unhatched egg. Therefore, she cannot possibly know the use of the
nest with its eggs and store of food. She has no "reason" for building
the nest, no ulterior purpose, but is impelled to build the nest,
simply and solely for the sake of doing just that thing. Thus instinct
is contrasted with calculated or reasoned action as well as with
learned action. Calculated action is based on knowledge of cause and
effect, and this knowledge is acquired by the individual in the course
of his experience; but instinct is not based on the individual's
experience, but only on his native constitution.
The case of the baby eating is exactly the same as that of the wasp.
The baby has not learned to eat, he knows nothing of the use of food
and therefore has no ulterior purpose in eating, he does not reason
about the matter, but eats simply because hunger is a native impulse
to eat. {106} Eating is an end in itself to a hungry baby, and not a
means to some further end; and that is what eating continues to be
even to the hungry adult, however much he may learn about the use of
food in maintaining life. From a broad philosophical point of view,
instinct may be seen to work towards some great end, such as the
preservation of the individual or the propagation of the race, but
from the individual's own point of view, it is directed simply towards
the performance of some particular act, or the accomplishment of some
particular result.
If instinct, as a collective term, means native behavior, "an
instinct" is a unit of such behavior. Or, it is some unit of native
organization that equips the individual to behave in a certain way.
Different species of animals have different instincts, i.e., they are
differently organized by nature. The differences of organization lie
partly in the equipment of sense organs, partly in the equipment of
motor organs, and partly in the nerves and nerve centers that, being
themselves aroused by way of the sense organs, in turn arouse the
motor organs.
The dependence of instinct on sensory equipment becomes clear when we
think of animals possessing senses that human beings lack. The
instinct of dogs to follow the scent depends on their keen sense of
smell. Bees have something akin to a sense of taste in their feet, and
follow their own trails by tasting them. Fishes have special sense
organs along their sides that are stimulated by water currents, and it
is in response to this stimulus that the fish instinctively keeps his
head turned upstream.
The dependence of instinct on motor equipment is still more obvious.
The flying instinct of birds depends on the possession of wings, and
the swimming instinct of the seal depends on the fact that his limbs
have the peculiar form of flippers. The firefly instinctively makes
flashes of light, {107} and the electric eel instinctively discharges
his electric organ and gives his enemy a shock.
But the core of an instinct is to be sought in the nerve centers,
since it is there that the coördination of the muscles is
accomplished. A wing or flipper would be of no use unless its muscles
were excited to action by the nerve centers, and it would be of very
little use unless the nerve centers were so organized as to arouse the
muscles in a certain combination, and with a certain force and rhythm.
In terms of the nervous system, an instinct is the activity of a team
of neurones so organized, and so connected with muscles and sense
organs, as to arouse certain motor reactions in response to certain
sensory stimuli.
The Difference Between an Instinct and a Reflex
What we have said regarding instinct thus far could equally well be
said of reflex action. A reflex is a native reaction, and it is taken
care of by a team of neurones in the way just stated. We might speak
of a reflex as "instinctive", using this adjective as equivalent to
"native"; but we should shrink for some reason from speaking of the
pupillary reflex to light as an instinct, or of the "knee jerk
instinct", or the "swallowing instinct", or the "flexion instinct".
There is some difference between the typical reflex and the typical
instinct, though it is not very obvious what the difference is.
The typical reflex is a much simpler act than the typical instinct,
but it is impossible to separate the two classes on this basis. At the
best, this would be a difference of degree and not of kind. Among
reflexes, some are simpler than others, but even the simplest is
compound in the sense of being a coördinated movement. The knee jerk
is simpler than the flexion reflex, and this is simpler than the
scratch {108} reflex, which consists of a rapid alternation of flexion
and extension by one leg, while the other is stiffly extended and
supports the trunk. Coughing, which would be called a reflex rather
than an instinct, consists of a similar alternation of inspiration and
forced expiration, and swallowing consists of a series of tongue,
throat and gullet movements. These compound reflexes show that we
cannot accept the simple definition that is sometimes given for an
instinct, that it is a compound of reflexes. Such a definition would
place coughing and swallowing among the instincts, and so do violence
to the ordinary use of the word. In point of complexity, we find a
graded series ranging from the pupillary reflex at one extreme to the
nesting or mating instinct at the other, and no sharp line can be
drawn on this score between the reflexes and the instincts.
Another distinction has been attempted on the basis of consciousness.
Typically, it may be said, a reflex works automatically and
unconsciously, while an instinct is consciously impulsive. The reflex,
accordingly, would be an unconscious reaction, the instinct a
conscious reaction. But this distinction also breaks down on
examination of cases. The pupillary reflex, to be sure, is entirely
unconscious. But the flexion reflex is a little different. When
unimpeded, it occurs so promptly that we are scarcely aware of the
painful stimulus before the reaction has occurred. But let the
reaction be hindered--either voluntarily or, for instance, by the foot
being seized and held--and a strong conscious impulse is felt to pull
the leg away; so that here the flexion reflex would belong among the
instincts, according to the proposed distinction.
Similar remarks would apply equally well to coughing, since a strong
impulse to cough is felt if the coughing movement is checked.
Sneezing, a protective reflex, is usually a slow reaction, giving time
for a conscious impulse to {109} sneeze before the reaction takes
place. The same is true of scratching and of swallowing, and of a
number of other reflexes. In short, it is impossible to draw a
satisfactory line between reflexes and instincts on the basis of
conscious impulse.
These cases point the way, however, to what is probably the best
distinction. It was when the flexion reflex was _delayed_ that it
began to look like an instinct, and it was because sneezing was a
_slow_ response that it had something of the character of an instinct.
Typically, a reflex is a prompt reaction. It occurs at once, on the
occurrence of its stimulus, and is done with. What is characteristic
of the instinct, on the contrary, is the persisting "tendency", set up
by a given stimulus, and directed towards a result which cannot be
instantly accomplished.
An Instinct Is a Native Reaction-Tendency
We would propose, then, to consider an instinct as an inner
adjustment, or tendency to reaction. It is this, rather than just a
reaction. When a stimulus promptly arouses a reaction, and that ends
the matter, we speak of reflex action--provided, of course, the
connection between stimulus and response is native. But when a
stimulus sets up a tendency to a reaction that cannot be immediately
executed, or towards an end-result which cannot immediately be
reached, and when the tendency so aroused persists for a time in
activity, and gives rise to preparatory reactions, then we speak of
instinct.
The "broody" hen makes a good picture of instinct. When in this
condition she responds to a nestful of eggs, as she does not at other
times, by sitting persistently on them and keeping them covered. She
is in a certain "organic state" that facilitates this response. In the
absence {110} of any nestful of eggs, she shows a peculiar restless
behavior that indicates to one who knows hens that this one "wants to
set." The tendency that has been awakened in her cannot be satisfied
by any momentary act, but persists and governs her actions for a
considerable period.
The nesting instinct of birds affords a still more complete example.
The end-result here, the finished nest, cannot be instantly had, and
the pair of birds keep on gathering materials and putting them
together until this end-result is present before their eyes. It is not
necessary to suppose that the birds have any plan or mental image of
what the nest is to be like; probably not. But their state, in the
nest-building season, is such that they are impelled to build, and the
tendency is not quieted till the completed nest is there.
The mating instinct, in unsophisticated members of the human species,
is another perfect example. So is the hunting instinct in a dog; when
this instinct is aroused, the animal makes a lot of movements of
various sorts, responses to various particular stimuli, but evidently
these movements are not sufficient to quiet the tendency, for they
continue till the prey is captured. The behavior of a gregarious
animal when separated from his fellows shows the same sort of thing.
Take a young chick out of the brood and fence it away from the rest.
It "peeps" and runs about, attacking the fence at different points;
but such reactions evidently do not bring satisfaction, for it varies
them until, if a way out of the inclosure has been left, it reaches
the other chicks, when this series of acts terminates, and gives way
to something quite different, such as pecking for food.
The persisting tendency does not produce the series of movements all
by itself, but, as was explained in speaking of tendencies in general,
coöperates with sensory stimuli in producing them. Clearly enough, the
nest-building bird, {111} picking up a twig, is reacting to that twig.
He does not peck at random, as if driven by a mere blind impulsion to
peck. He reacts to twigs, to the crotch in the tree, to the half-built
nest. Only, he would not react to these stimuli unless the nesting fit
were on him. The nest-building tendency favors response to certain
stimuli, and not to others; it facilitates certain reactions and
inhibits others. It facilitates reactions that are _preparatory_ to
the end-result, and inhibits others.
Fully and Partially Organized Instincts
Insects afford the best examples of very highly organized instincts.
Their behavior is extremely regular and predictable, their progress
towards the end-result of an instinct remarkably straightforward and
sure. They make few mistakes, and do not have to potter around. By
contrast, the instincts of mammals are rather loosely organized.
Mammals are more plastic, more adaptable, and at the same time less
sure; and this is notably true of man. It would be a mistake to
suppose that man has few instinctive tendencies; perhaps he has more
than any other creature. But his instinctive behavior has not the
hard-and-fast, ready-made character that we see in the insects. Man is
by all odds the most pottering, hem-and-hawing of animals. Instinct
does not lead him straight to his goal, but makes him seek this way
and that till he finds it. His powers of observation, memory and
thought are drawn into the game, and thus instinct in man is
complicated and partly concealed by learning and reasoning.
For example, when an insect needs a nest, it proceeds in orderly
fashion to construct a nest of the pattern instinctive to that species
of insect; but when a man needs a home, he goes about it in a
variable, try-and-try-again {112} manner, scheming, experimenting,
getting suggestions from other people, and finally producing--a
dugout, a tree house; a wigwam, a cliff dwelling--something that
differs altogether from many other human habitations, except in the
fact that it is a habitation and thus satisfies a need which is
undoubtedly as instinctive in man as in the insect.
A fully organized instinct is one where the necessary preparatory
reactions are linked up closely with the main reaction-tendency, so
that, once the main tendency is aroused to activity, the preparatory
reactions follow with great sureness. The main team of neurones is
closely connected with the subordinate teams that give the preparatory
reactions; and these connections do not have to be acquired by
experience and training, but are well formed by native growth. Just
the right preparatory reactions are linked to the main tendency, so
that the whole series of acts is run of
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